A MONOGRAPH:

MORPHOLOGY or FLOWER PRIMORDIA]?
’ 0-5 SELECTED wooov PLANTS

 

THESIS

This is to certify that the
thesis entitled

A Monograph: Morphology of Flower Primordia
of Selected Woody Plants

presented by

Edwin D. Carpenter Jr.

has been accepted towards fulfillment
of the requirements for

_Eh_D_ degree in Mil—Ire

Major professor

MW 14M-

0—169

LIBRARY

Michigan State
" University

 

 

 

 

 

ABSTRACT

A MONOGRAPH: MORPHOLOGY OF FLOWER PRIMORDIA
OF SELECTED WOODY PLANTS

by Edwin David Carpenter, Jr.

An investigation was conducted to determine the time of flower
bud initiation in selected woody ornamental species which were grow-
ing in an existing environment and normally flower in the spring,
summer, autumn and late winter at East Lansing, Michigan”

Plants of Cornus {gas L., Forsythia o_y'a_ta Nakai., Spiraea
thunbergi Sieb., Prunus glandulosa Thunbo, Viburnum lentago L. ,
Pyracantha coccinea Roem. lalandii Dipp., 139i multiflora Thunbi,
Viburnum dentaturn L.,, Hibiscus syriacus L., Indigofera potanini
Craib., Clematis paniculata Thunb., Hamamelis virginiana La, and

 

Hamamelis vernalis Sargn were selected to represent 1 of 4 arbitrary
seasons: spring (March to May); summer (June to August); autumn
(September to November); and winter (December to February)” All
plants were located on the campus of Michigan State University
(latitude 420 47‘ N, longitude 840 36' W) under similar environmental
conditions.

Collections of both vegetative and floral buds were made bimweekl‘y
from March 3 to October 27, 1962. In 1963, collection intervals Were
spaced 3 to 7 or 10 days apart throughout the growing season”

After collection, the buds were trimmed, processed in paraffin
before median microscopic sections were cut and mounted for exami—

nationo

    

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Edwin David Carpenter, Jr.

Field observations included flowering dates, date of leaf expansion,»
date of fruit maturation, and the beginning of vegetative growth. During
1962, 1963 and 1964 field observations were recorded 3 times per week
throughout the growing season.

In those plants on which the flowers developed directly from
initiation to anthesis, it was found that Clematis paniculata Thunb.
initiated flower buds during the period of minimum vegetative growth and

that Hamamelis virLiniana L.,, Hibiscus syriacus L., and Rosa multiflora

 

Thunb. initiated flower buds during the period of maximum vegetative
growth,

In plants where flower development was interrupted by a rest
period, all flowers were shown to be present at the time of dormancy
except for Pyracantha coccinea Roem, lalandii Dipp. and Viburnum
dentatum L, Both of these plants showed inflorescence primordia at
dormancy and individual flower initiation began the following spring,
Cornus r_n_a_s_ Lu, Forsythia ov_ata Nakaig, Hamamelis vernalis Sargu,
Prunus glandulosa Thunb,, Spiraea thunbergi Sieb, and Viburnum
lentago La flowers were formed at the time of dormancya lndigofera
potanini Craib, initiated flowers throughout the growing season and
miniature racemes could be found in various phases of development
over-winter.

For the most part, floral structures initiated in acropetal success—
ion, Hibiscus syriacus L, produced involucre bracts first, then sepals,
staminal column and petals simultaneously or the petals somewhat later,
and lastly the carpels, The order of appearance in the 12 other plants
was found to be sepals, petals, stamens, and carpels,

The text is accompanied by 11 figures of camera lucida drawings

and photomicrographs, and 16 tables,

     

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A MONOGRAPH: MORPHOLOGY OF FLOWER PRIMORDIA
OF SELECTED WOODY PLANTS

By

Edwin David Carpenter, Jr.

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements

for the degree of
DOCTOR OF PHILOSOPHY
Department of Horticulture

1964

 

 

DEDICATED TO

Dorothy Lee Carpenter

 

 

 

ACKNOWLEDGEMENTS

To give the proper thanks for all assistance received in this
work is more than words can express; for help and encouragement,
other than financial, are often subtle and beyond definition.

To the chairman of the guidance committee, Dr. Donald P.
Watson, who directed the work and the writing of this thesis, the
author's most sincere appreciation. Thanks are expressed to the
members of the committee, Drs. J. H. Beaman, L. W. Mericle
and C. L. Hamner as well as to Dr. C. M. Harrison; and especially
to Mr. C. E. Lewis for his help and suggestions.

 

TABLE OF CONTENTS

INTRODUCTION .

REVIEW OF LITERATURE .

Tree Fruits . . . . . . . .
Nut Trees . .
Evergreen Fruits .

Small Fruits .

Woody Ornamentals

MATERIALS AND METHODS

RESULTS.

Clematis paniculata Thunb.
Cornus mas L. . . .

Forsythia ovata Nakai.
Hamamelis vernalis Sarg.

 

 

Hamamelis virginiana L.

Hibiscus syriacus L. . . .

Indigofera potanini Craib. . . . . .
Prunus glandulosa Thunb. . . . . . . . . . .
Pyracantha coccinea Roem. lalandii Dipp.
Rosa multiflora Thunb. . . . . . . . . . . .
Spiraea thunbergi Sieb.

Viburnum dentatum L.

Viburnum lentago L. . . . . . . . . .

 

 

CONCLUSION .

LITERATURE CITED . .

Page

H

WHOOOU'I #3

‘—l.—J

19

LIST OF TABLES

TABLE Page
1. Geographical Differences of Flower Bud Initiation. . 7
2. Literature Synopsis. . . . . . . . . . . . . . . . . . 22

3. Growth Characteristic of Clematis paniculata Thunb. Z4
4. Growth Characteristics of Cornus mas L. . . . . . . 28

5. Growth Characteristics of Forsythia ovata Nakai . . 32

 

6. Growth Characteristics of Hamamelis vernalis Sarg. 36

7. Growth Characteristics of Hamamelis virginiana L. . 40

 

8. Growth Characteristics of Hibiscus syriacus L. . . . 42
9. Growth Characteristics of Indigofera potanini Craib . 47

10. Growth Characteristics of Prunus glandulora Thunb . 52.

11. Growth Characteristics of Pyracantha coccinea
Roem.lalandiiDipp................. . 56

12.. Growth Characteristics of IE multiflora Thunb. . 6O

13. Growth Characteristics of Spiraea thunbergi Sieb. . 64

14. Growth Characteristics of Viburnum dentatum L. . . 69

15. Growth Characteristics of Viburnum lentago L. . . . 73

16. Summary of vegetative growth, flower bud formation
andflowering.....................77

v

 

1v '1 I‘- C:

LIST OF FIGURES

FIGURE Page

1. Stages in the development of flower buds of
Clematis paniculata Thunb. . . . . . . . .. . . . . . 25

2. Stages in the development of flower buds in Cornus
masL 29

3. Stages of development in flower buds of Forsythia
ovataNakai...................... 34

4. Stages of development of the flower buds in
Hamamelis vernalis and I-_l. virginiana L. . . . . . 38

5. Phases of flower bud development in Hibiscus

syriacus L. . . . . . . . . . . . . . . . . . . . . . 44
6. Flower bud development in Indigofera potanini

Craib. . . . . . . . . . . . . . . . . . 49
7. Stages in the development of flower buds of Prunus

glandulosa Thunb. . . . . . . . . . . . . . . . . . . 53

8. The development of floral buds in Pyracantha

coccinea Roem. lalandii Dipp. . . . . . . . . . . . 57
9. Development of flower buds in Rosa multiflora
Thunb. . . . . . . . . . . . . . . . . . . . . . . . . 62

10. Stages in the development of Spiraea thunbergi

Sieb. flower buds . . . . . . . . . 66
ll. Stages of flower development in Viburnum dentatum
L. and Viburnum lentago L. . . . . . . . . . . . . 71

vi

 

 

 

FIGURE

LIST OF FIGURES

Stages in the development of flower buds of
Clematis paniculata Thunb. . . . . . . . . . . .

Stages in the development of flower buds in Cornus
masL

Stages of development in flower buds of Forsythia
ovataNakai. . . . . . . . . .

Stages of development of the flower buds in
Hamamelis vernalis and H. virginiana L. . . . .

Phases of flower bud development in Hibiscus

syriacus L.

Flower bud development in Indmigofera potanini
Craib. . .

Stages in the development of flower buds of Prunus
glandulosa Thunb. . . . .

The development of floral buds in Pyracantha
coccinea Roem. lalandii Dipp. . . . . . . . . .

Development of flower buds in Rosa multiflora
Thunb.

Stages in the development of Spiraea thunbergi
Sieb flower buds . . . . . .

Stages of flower development in Viburnum dentatum

L. and Viburnum lentago L.

vi

Page

25

2.9

34

38

44

49

53

57

62

66

71

 

 

“tr: amen

INTRODUCTION

During the first half of the twentieth century Goff (1899, 1900,
1901), Drinkard (1909), Bradford (1915), Tufts and Morrow (1925),
Ranker (1926), Rassmussen (1929), Aaron (1936), and Pickett (1942)

 

produced a wealth of information concerning the time of flower bud
initiation of apples, pears, peaches, cherries, plums, apricots and
almonds. Their findings have been the basis of establishing times and
methods of fertilizing, pruning, cultivating and reducing winter injury
(Ruth, 1921; Harley, Masure and Magness, 1932; Crane and Dodge,
1935; Roberts, 1937; and Edgerton and Harris, 1950)°

Very little information is available, however, concerning the
time of flower bud initiation of woody plants that are not grown prim-
arily for fruit production. It was generally agreed before 1900 that
most trees in temperate climates which flowered early in the year
produced flower buds at some time during the previous season.

Dr. Beale in 1656 stated that "before December by the bluntness
of the bud, you may discover what branch will bear fruit the next season
immediately following" (Davis, 1957). Thatcher in 1822 identified the
time, and even the cause, more precisely when he said, “the blossom
buds are formed by the first sap betWeen April and June and are filled
by the second sap between July and October" in the apple (Davis, 1957).

The flowering process is only a single response, is inherited, and
involves the reaction of genes and their products to the environment
(Salisbury, 1963). This is evident from the fact that a plant commonly
flowering in one location may flower at a different time in another

location even though the environmental requirement has not changed.

The study of flowering in recent years has been conducted from
the standpoint of controlled environments and the influence of chemicals
(Gartner and McIntyre, 1957; Downs and Piringer, 1958; Boodley and
Mastalerz, 1959; MacLean, 1962; Cannon and Gartner, 1963). Yet
purely ecological studies of the flowering process have been few; the
woody plants of the street, garden and forest having been studied the
least.

The initiation of flowers is a change over from the indeterminate
to the determinate type of growth. Thus, the initiation of floral organs
exchanges the immortality potential for the possibility of combining
germ plasm in order to produce a new individual or to perpetuate the
original individual. The time of flower initiation depends somewhat on
the rate of the preceding vegetative growth. The conditions which in-
fluence this rate of growth may, and do, cause differences in the time
of flower formation without having affected initiation in any specific
manner (Lang, 1952).

Grainger (1939), working in England, was perhaps the first to
conduct detailed investigations on flower initiation in ornamentals,
especially of English wild woody plants now used as ornamentals.
Reports of flower initiation in Gaultheria species (Chou, 1952),
Populus deltoides Marsh. and 1:. tremuloides Michx. (Nagaraj, 1952),
Michelia fuscata Blume (Tucker, 1960), Cydonia oblonga Mill. (Zeller,
1960), Pyracantha coccinea Roem. lalandii Dipp. (Reisch, Chadwick
and Hildreth, 1961) and Syringa species (Sijtesema, 1962) have since
been published.

The present investigation was undertaken to determine the time
of flOWer bud initiation in selected woody ornamental species growing
in an existing environment. They were selected to represent species
that flOWer in early spring, summer, autumn and winter. It was de—

signed to obtain information useful for the augmentation and timing

 

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cultural practices such as nutrition, pruning, and irrigation. It was
hoped that knowledge about natural potentials possessed by such species
might further extend the cultivation of these plants to localities outside
their native habitats. It was also intended that plant breeders might
find such information useful for selecting suitable parents and improv-

ing existing species and cultivars.

 

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REVIEW OF LITERATURE

In the 19th century Hofmeister, Webb, Pfeffer and Goebel studying
the order of succession of floral parts, observed that flowers of angio—
sperms developed in acropetal succession. Hofmeister (Coulter and
Chamberlain, 1903) concluded for instance that carpel primordia of
M, Potentilla, and m appeared before stamens reached their full

number, and that sepal primordia of Hypericum calycinum L. appeared

 

after the primordia of the stamens. Pfeffer (1872) showed that the
petal primordia appeared after that of the stamens in Primulaceae and
that each petal apparently formed from the dorsal surface of a young
stamen. Goebel (1887) working with papilionaceous flowers of
Leguminosae found that the anterior median sepal appeared first followed
immediately by those to the right and left. Before the last two sepals
Were evident, the obliquely posterior petals were visible and these were
followed by the 3 other petals in the same order as the corresponding
sepals. Webb (1902) explained the order of succession in Astilbe to be
sepals, inner stamens, carpels, outer stamens and petals. Thus,
acropetal succession of certain cycles followed by basipetal succession
of the remaining cycles became evident. Additional modifications of

succession can be found in Compositae, Disacaceae, Valerianceae,

 

Rubiaceae (appearance of sepal primordia after that of the stamens and
carpels), and Cruciferae Juss. (petal primordia last to appear).

By cutting buds of Sanguinaria canadensis L. Foersts (1891) found

 

that all floral parts were clearly recognizable in mid—August, that the
flower bud cluster of Cornus canadensis L. and the raceme of flower

buds of Pyrola elliptica Nutt. were clearly distinguishable at this time.

 

Objective research regarding the time of flower bud initiation
seemed to be lacking until Goff's work in Wisconsin in 1899. Goff
stated as a purpose for his studies: "No systematic investigation seems
to have been made that gives us any definite knowledge as to the time
when the development of the flower actually begins, the rate at which it
progresses or the period through which it continues in any of our fruit
bearing plants. This information is important because it will enable us
to make definite experiments on the effect of special practices upon the
formation of flowers. " In addition to presenting factual evidence relat—
ing to the time of floral initiation, Goff‘s researches emphasized a

technique which has had wide application.

Tree Fruit

During the 1899 season, Goff found that floral growth started
about the same time as vegetative growth ceased elongation. Flowers
of apple (w sylvestris Mill. ), plum (Prunus domestica L.) and
pear (m communis L.) were observed to have started growth several
weeks before fruit maturation. FlOWer growth of the cherry (Prunus
m L. ), however, was observed to be almost simultaneous with fruit
maturation. Goff (1899) observed flower primordia of the 'Hoadley'
apple on June 30, 'Rollingstone' plum on July 8, “Aitken' plum on
August 9, 'Wilder Early' pear on July 21 and 'King's Amarelle‘ cherry
on July 11 under natural environmental conditions at Madison, Wisconsin.
Acropetal succession was established in all cases.

The apple and pear studies were continued in 1900. Since Goff
had removed all of the 'Hoadley' apple flower buds the previous season
(1899), these supposedly did not have any flower buds, but many swollen
buds of flower bud size were visible in March of 1900. These dissected

buds contained flowers. The first evidence of flower formation observed

 

 

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in the 'Hoadley‘ apple and 'Wilder Early‘ pear was in early September ,
1900 but Goff apparently felt that the lateness of the season in 1900
compared to 1899, may have been caused by the removal of the plumpest
buds for microscopic study. Goff also observed that flower formation
in buds of the apple and pear continued until October during 1900. From
these observations he proposed that flower formation may occur during
two periods-—early summer and mid-auturnn until the beginning of cold
weather. With the 'Bokara' peach (Prunus persica Batsch. cultivar)
Goff observed that flower formation did not begin until late September
with the advent of cool nights.

Perhaps stimulated by the findings of Goff the time of flower

initiation and differentiation has been investigated in the last few years

 

in a wide range of plant species and cultivars under many varied climatic
and geographical conditions. In addition, dissection and classification
techniques have been evolved with which comparisons of a quantitative
nature can be made among responses under various conditions (Davis,
1957). Table 1 summarizes the findings of several of these workers.

Ranker (1926) did not find a second period of flower bud initiation
in the “Delicious' apple, except in isolated cases where buds developed
on second-growth wood. Furthermore, Heinicke (1963) believed that
apple flower buds initiated “relatively late in the season“ were likely to
be abnormal or partially developed. If these buds remained and formed
fruit, the resultant fruits were usually small or misshapen.

In England similar results have been observed. Ball (1927) indicated
that the 'Victoria' and 'Cambridge Gage' plums initiated flowers from
mid—July to early August. Gibbs and Swarbrick (1930) found that apple
(M sylvestris Mill.) flower buds were initiated at different times
depending upon the location of the bud on the tree. Distinct flower
primordia Were found on July 2 in buds taken from 2=-=year and 3—year

single spurs. Axillary buds on l~year wood were not collected until the

    

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Table 1: Geographical Differences of FloWer Bud Initiation

 

 

Fruit Date Area
‘Oldenburg‘ apple June 30 Virginia
'Kieffer' pear July 22 Virginia
'Luster‘ peach August 5 Virginia
'Whitaker‘ cherry September 4 Virginia
'Louis Phillippe' cherry September 10 Virginia
P1um--American group September 4 Virginia

Japanese group September 10 Virginia (Drinkard,

1909—1910)
"Yellow Newton' apple July 5 to 10 Oregon (Bradford, 1915)
'Gravenstein' apple June 11 California
'Bartlett' pear June 21 California
'Elberta‘ peach June 30 California
'Royal Ann‘ cherry July 3 California
‘Early Richmond' cherry July 12 California
'French' plum August 15 California
'Wickson' plum August 15 California
'Royal' apricot August 10 California (Tufts and
'Nonpareil’ almond September 9 California Morrow, 1925)
'Delicious' apple June 19 Utah (Ranker, 1926)
‘Baldwin' apple July 15 New Hampshire
'Mclntosh' apple July 22 New Hampshire (Rassmussen,
' 1929)
'Mclntosh' apple July 14 Pennsylvania (Aaron, 1936)
(spur buds only)

Peach - ‘Mayflower' September 13 Texas

'Early Rose Cling' August 15 Texas

‘Dr. Burton‘ August 10 Texas

'Frank' September 3 Texas

‘Dee Lee Cling' September 13 Texas

“late" unnamed September 13 Texas

'Smith' (Honey) September 13 Texas (Pickett, 1942)

 

      

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first Week of August but a few buds showed the presence of flower
primordia. Thus, both Gibbs and Swarbrick (1930) and Magness (1916)
agreed that the axillary buds did not initiate flowers until one month

after the spur buds.

In Manchuria, flower bud initiation in the 'Jonathan‘ apple occurred

during the first ten days of July (Watanabe and Yasaka, 1930). Thus, the

period of flower bud initiation in Manchuria closely resembled the time
of initiation of buds in Oregon (Bradford, 1915). Apple bud initiation in
the Malatya district of Turkey occurred about June 20 according to
Ulkumen (1940), followed by the pear and by July 30 for the apricot
(Prunus armeniaca L. ). Ushirozawa and Fukushima (1950) determined
that apple buds formed in late June to late August in Japan and found .
the following: ‘Yellow Transparent‘, ‘Early McIntosh' and 'Mclntosh
Red' apples formed flower buds in the early part of the period; 'Golden
Delicious' and 'Newton Pippin‘ formed flower buds during the middle
part of the period; and the ‘Delicious‘, ‘Winesap‘ and 'Jonathan' formed
flower buds during the latter part of the period.

Hirai, Nakagawa, Nanjo and Hirata (1961) observed in Japan that

flower initiation in Prunus persica Batsch. 'Okubo' varied among 20

climatic regions despite differences of tree age and cultivation methods.

Floral initiation was found to occur first on July 10 in the southern
districts of Ehime, Kochi, Fukuoka and Miyazaki. Initiation occurred
rather uniformly until the last evidence of initiation appeared on July
30 in the northern districts of Fukushima, Yamagata, Niigata, Ishikawa

and Nagano .

Nut Trees

Gardner, Bradford and Hooker (1952) state that Albert (1894, in

Germany) found evidence of catkins in the filbert (Corylus avellana L.)

,

 

 

on June 10 before the embryonic leaves were laid down, but the female
blossoms Were not observed until early September. In the beech (Figlis
L. species) Albert did not find flower buds until after leaf fall began

but he indicated that initiation must have occurred much earlier since
the pollen mother cells had already formed in the anthers.

Shuhart (1927) and Isbell (1928) observed that the pistillate flowers
of the pecan (CM illimoiennis Marsh.) Were initiated in late winter or
early spring at the time when vegetative buds began to swell. These
pistillate buds continued development until approximately 10 or more
leaves had unfolded. At this time the pistillate flowers became visible.
Staminate flowers were observed to initiate later in the season in the
lateral buds. They do not complete their development or shed pollen,
however, until the following year. Staminate flower initiation has been
found to occur on secondary shoots rather late in the summer (Isbell,

1928).

Evergreen Fruits

In Gigs species, flower bud initiation was keyed more closely
to periods of active growth and relative quiescence than to calendar
dates (Abbott, 1935; Randhawa and Dinsa, 1947; Singh and Dhuria, 1960).
Thus, flower initials were generally not seen until approximately the
time at which the flower shoot emerged from the bud (Furr and Armstrong,
1956).

Smock (1937) stated that the flower development of the loquat
(Eriobotrya japonica (Thunb.) Lindl.) was much like that of the apple
flower development which was acropetally oriented. Falta Del Bosco
(1961) in Sicily found that in most cultivars of loquat flower initiation
began during the first 20 days of June and that in later flowering cultivars

flower initiation began the latter part of July. In India, Bajpai and Shukla

 

 

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(1962) found two periods of flower initiation; the first being in July to
mid-August and the second from the second week of October to the first
week of December.
Floral initiation in the mango (Mangifera M L.) in Florida
occurred shortly before the end of October in the Haden, Cambodiana,
Brooks and Turpentine cultivars (Mustard and Lynch, 1946). Dormancy
has not been found to occur between the time of floral initiation and the
time of inflorescence expansion. These data agreed fairly well with
observations on the "Langra' mango in India (Sen and Mallik, 1941).
As explained by Hartman (1951) Morettini first found evidence of
olive (CE europaea L.) f10wer primordia during the first half of ‘
March—-2;— months before flowering-—in Italy. Savastano and Marcucci
indicated that flower initiation started at the end of the winter--10 to 15
days before flowering, while in Portugal, De Almeida found that flower
bud initiation occurred in the olive cultivars 'Galega‘ and 'Verdeal'
during early February followed by the bloom in May (Hartman, 1951).
Further evidence of the similarity in time of olive flower bud
initiation was found by Hartmann (1951) in California. He identified
initiation in March-—approximately 8 weeks before full bloom. He ob-
served very little difference between the cultivars 'Mission‘, ‘Manzanillo'
and ‘Swillana' or between the 5 locations in which they were growing.
In addition, Hartmann observed no change in the buds from the time they
first were recognizable in June until flower parts appeared the following
March.
In the avocado (Persea american Mill.) Reece (1942) found that
floral initiation continued over a period of months during the part of the

winter when leaf formation and gorwth were at a minimum.

 

.. 1..

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5

. Small Fruits

In 1900 Goff found flower initials in both the young runners and
parent plants of the ‘Clyde' strawberry (Fragaria chiloensis Duchesne.)
on September 20, with the advent of cool nights.

The time of flower bud formation in the currant (11353 L. species)
varied with the cultivar--‘Pomona‘, July 8; 'White—Grape', October 30;
‘Black Victoria', August 3 (Goff, 1901). In the 'Downing' gooseberry

(Ribes grossularia L.) and cranberry (Vaccinium macrocarpon Ait.)

 

floral initiation was clearly visible in late August and early to mid-
September, respectively. Goff‘s observations on plants whose flower
buds were not readily distinguishable in the autumn (quince, raspberry
and blackberry) showed ”embryo" flowers to be present with the
commencement of dormancy. The grape (m L. species), red rasp-
berry, blackberry (Rpfl L. species) not only exhibited these same
”embryo" flowers but in addition an “embryo" branch.

MacDaniels (1922) found W L. and Rig: L. species to vary
considerably in regard to flower bud initiation in New York. 'Gherry
Red‘ currants were shown to initiate flowers in mid=August. A slight
variation in the time of floral initiation in the ‘Houghton' and 'Golumbus‘
cultivars of gooseberry was found to be from mid=August to 10 to 14
days later, respectively. Flower initials were observed by MacDaniels
in the 'Snyder' blackberry in mid—August just as found by Goff (1901),
The red raspberry and 'Columbian' purple=cane raspberry showed only
imperfect initiation in the autumn. Early October seemed to be the
time of flower initiation in the ‘Gurnberland‘ black raspberry.

In Scotland, Mathers (1952) found that floral initiation in R_u_l£s_
idaeus L. cultivars 'Lloyd George', 'Malling Promise‘ and ‘Malling
Landmark‘ began in mid-September and by the last week of September

a definite inflorescence axis was terminated by the first formed flower.

 

Further development was observed to be basipetal in an irregular spiral
with rapid development occurring during October.

Further investigation in Scotland on the genus M L. (Robertson,
1957) showed that in the red raspberry, purple-cane hybrid raspberry
and loganberry early flower initiation and considerable further develop-
ment occurred in the autumn. Whereas, in the blackberry and black
raspberry development of flower primordia occurred mainly in the
spring.

Lacroix (1926) reported that the cranberry (Vaccinium macrocarpon

 

Ait.) flower primordia were first Visible during the middle of August in
Massachusetts. The incipient flower started as a minute lateral "out—
pushing”, and developed acropetally. Cranberry flower buds passed the
winter without stamens or carpels; stamens becoming evident in mid—
April and carpels from early to mid—May.

Floret formation in the lowbush blueberry (Vaccinium angustifoliurn

 

Ait.) was initiated during June (Bell and Burchill, 1955). During July,
floral parts differentiated in acropetal succession. The miniature,
epigynous floret was thus completely formed by the first of August.
Active growth, including the initiation of meiosis did not generally start
until April of the following year. Meiosis was completed in the anthers
by the first week of May and in the carpel approximately 1 Week late,

but Eggert (1957) concluded that flower initiation apparently did not occur
until after the death of the terminal growing point.

In V_i_t_is labruscana Bailey 'Concord‘ cluster initiation occurred in
the young buds and continued in newly formed buds throughout the grow—
ing season (Snyder, 1933). Snyder stated that “cluster primorida were
initiated in newly forming buds” simultaneously with the ”development of
the early buds, so that by the end of the growing season all buds on the

shoot contained approximately the same number of primordial clusters. “

 

u: . i" - ‘a-I: . I. . ' ' ' .1‘ -- " I"-'..‘."I':'iGi but =;

_n _ '.‘llgm

The first flower clusters have been shown to be evident in early June.
Growth of this cluster was rather rapid until mid-July when both cluster
and shoot growth slowed down. At this time the secondary clusters
continued to branch so that numerous tertiary clusters were discernible
at the end of the growing season. The differentiation of definite floral
structures occurred in an acropetal order immediately following initiation
of the flower clusters. The first evidence of flower formation occurred
approximately in late April—-at the time of bud swelling--appearing
first and determinately in basal sub-clusters (Snyder, 1933).

Winkler and Shemsettin (1937) indicated that cluster primordia of
Ms vinifera L. ‘Sultanina‘ began to initiate during the first week of
June in California. This primordium appeared as a blunt, rather broad
outgrowth of the bud apex. The formation of a bract was the first indi-
cation that division of the primordial cluster had occurred and took
place a week to 10 days after the cluster was initiated. Lateral clusters
were then initiated in the axils of these bracts. Thus, by the end of the
growing season the lateral surface of the primordial cluster was a mass
of bracts and branch primordia, the tendrils being initiated somewhat
later in the season.

Zeller (1960) agreed with Goff (1901) that flower initiation in the
quince (Gydonia oblonga Mill.) commenced in the autumn. In addition,
Zeller found that flower initiation and development occurred throughout

the winter .

Woody Ornamentals

In a study of greenhouse roses, Hubbell (1934) found that the first
evidence of flower initiation was seen 8 days after an axillary bud had
been made to assume the terminal position by removal of the terminal
bud. The first actual differentiation was evident on the ninth day when

sepal protuberances were observed. On the other hand, Laurie and

 

     

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Bobula (1938) found that the first evidence of initiation occurred 16 to
18 days after an axillary bud assumed the terminal position. Sepal
primordia were observed to be present in buds which had been in the
terminal position for 14 to 18 days. The order of succession was found
to be acropetally oriented.

Grainger (1939) studying various wild plants in England arranged
them by their type of flowering organization. In summary he found the
following:

1. Direct flowering plants where development from the first sign

of flower initials to anthesis was uninterrupted.

A. Direct flowering from the period of maximum vegetative
growth; flowers were initiated when leaf growth was at a
maximum (most common type).

Galluna vulgaris Hull. initiated June 30
flowered August 20

Erica cinerea L. initiated July 26
flowered August 20

Rosa canina L. initiated April 24
flowered June 25

B. Direct flowering from the period of minimum vegetative

growth; flowers were initiated in the late autumn or winter.

Lonicera periclymenum L. initiated March 12
flowered August 10

 

II. Indirect flowering plants==a rest interval between flower
formation and anthesis.

A. Indirect flowering from the period of maximum vegetative
growth; flowers were initiated toward the end of summer
and the flower buds were usually complete; flowering
occurred in the early months of the following year.

Vaccinium myrtillus L. initiated July 17
flowered following May 6

Salix caprea L. initiated July 9
flowered following March 11

Ilex aquifolium initiated August 15
flowered following June 17

B. Indirect flowering from the period of minimum vegetative
growth; flowers were initiated after the leaves have withered
and a period of dormancy follows after every organ was com-
plete. Many bulbs of horticultural value.

III. Cumulative flowering--flower initials were produced in regular
succession and all emerged together.

Plantago lanceolata L. initiated February 17
flowered May 15

Taraxacum officinale Weber. initiated November 9
flowered following April 30

 

IV. Climax flowering——a plant might be entirely vegetative for a
number of years and then entirely floriferous for a year.

Some species of Agava L.

Chou (1952) investigated the flower morphology of Gaultheria
procumbens L., g. ovatifolia Gray. and G. shallon Pursh. and found
flower initiation to occur during June at Chicago, Illinois. After initiation,
bud development proceeded rapidly with anthesis occurring in mid-July.
All floral parts formed in acropetal succession.

Working with Populus deltoides Marsh. and E. tremuloides Michx.,
Nagaraj (1952) found that the pistillate catkins appeared near the end of
the summer, whereas the staminate catkins arose toward the first part
of the summer. Both catkins remained as buds during the winter and
completed development early the following spring. The differentiation of
the individual flowers was essentially acropetally and spirally oriented.

Flower buds of Prunus yedoensis Matsum. were initiated approxi=~
mately August 8 in Japan (Kosugi, 1951-1952). Development continued

in acropetal succession rather rapidly until approximately November 1

 

-' .- ‘ - '- ._-. ..-. '. rum-1.
." l I.'.' .' ' . . .

16

When early anthers, without primary sporogenous tissue were present.
The differentiating sporogenous tissue was first observed on November
28 and pollen grains were completely developed by March 20. Carpel
development followed the anther development except that it was observed
to start about October 17.

Downs and Piringer (1958) in an experiment on the flowering
response to photoperiod in various Viburnum species found that photo-
period did not seem to control flower initiation, although marked differ—
ences in the extent of flower bud formation were evident among the

species. Viburnum burkwoodii Burkwood and X. chenaultii produced at

 

least 1 flower bud per plant; only one-quarter of the plants of V. carlesii
Hemal. formed flower buds; and \_/.j1_1_c_lEl_i_i Rehd. and X.p1icatum Thunb.
tomentosum Miq. did not form visible buds by August 20 when the experi-
ment was concluded. These authors indicated that those flower buds
which did form appeared to be single terminal buds tightly subtended by
bracts. However, upon microscopic study, each bract contained an
entire inflorescence and in addition, in the axils of each bud an individual
minute flower bud was produced. These minute flower buds remained
compressed and inconspicuous throughout the entire experiment.

Downs and Piringer (1958) conducted a field experiment using the
plants from the previous experiment with photoperiods. Five plants of
each species (except V. plicatum Thunb. tomentosum Miq.) from each
photoperiodic treatment were transplanted on August 20, September 17
and October 15. The small flower buds already visible were observed
to expand and appeared as enlarged bud clusters on plants of each group
6 Weeks after field planting. Certain buds of X. carlesii Hemal.
(previously under 8 and 12 hours of light) developed until the corolla tubes
expanded and colored; erractic anthesis often followed. By mid—
December marked differences in total flower=bud formation were noted.

\1. carlesii Hemal. and V. juddii Rehd. were found to form no flower

 

buds after planting in the field. However, the flower buds of V. burkwoodii
Burkwood and V chenaultii nearly doubled in number. Some of these new
flower buds may have formed in the greenhouse, but since plants on
longer daylengths were forming leaves at that time, these new flower buds
had more than likely been initiated in the field.

Flower initiation began in Syringa vulgaris L. 'Charles Joly' 29 to
35 days after anthesis of the first flowers in Ohio (Chadwick, Reisch
and Traylor, 1959), in contrast to June 21 in the Netherlands (Sijtesema,
1962).

In Michelia fuscata Blume. growing in a conservatory in St. Paul,
Minnesota, Tucker (1960) found that the vegetative apex was active the
entire year and that periodicity was shown by the type of axillary bud
produced. Axillary buds formed in the autumn and winter became vege—
tative whereas those axillary buds initiated in the spring and early
summer became floriferous. In each axillary flower bud, initiation of
bracts and perianth occurred in May and June; the stamens appeared
from July through August and the carpels developed from July through
September. Thus, there was evidence of acropetal succession of floral
parts, but all flower buds were found to be in different stages of develop—
ment at the same time.

Reisch, Chadwick and Hildreth (1961) found that the initiation of
the inflorescence of Pyracantha coccinea Roem. lalandii Dipp. was first
evident in late October with some inflorescent initiation occurring in
late March the following year. It was also observed that the greatest
development occurred during April with sepal primordia becoming evi-
dent in late April. This finding coincides with that of Girouard (1962)
who stated that most floral part primordial stages were not complete
until early May and that floral appendages differentiated over a period of

64 days in 1961 at Columbus, Ohio.

  

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The results of Girouard's (1962) examinations showed that sepals
were initiated on the flanks of the floral apex when the primordia
averaged 100 I4 in width. The 5 petal primordia arose simultaneously
when the sepal primordia were 50 1‘ high and the concave apical meri-
stem averaged 85 [.1 in width. In addition, the stamens apparently
originated simultaneously with the petals or quickly in succession since
few microscopic preparations showed petal primordia without stamen
primordia. Carpel formation followed closely with the result that locules
were present in the carpels at the time primary sporogenous tissue was
evident in the stamens. Microsporogenesis and megasporogenesis were

observed to be limited to the last 3 weeks preceding anthesis.

 

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MATERIALS AND METHODS

All plant materials were selected to represent 1 of the following
4 arbitrarily defined seasons: spring (March to May); summer (June to
August); autumn (September to November); and winter (December to
February). In addition, the following plants were chosen for a succession
of flowers during each of the 4 seasons but with a limited amount of over—

lapping of the flowering periods.

 

Spring early Cornus m_as Lo and Forsythia ovata
m
mid Spiraea thunbergi Sieb. and Prunus
glandulosa Thunba
late Viburnum lentago Lo
Summer early to mid Pyracantha coccinae Roema lalandii
Dipp.

Rosa multiplora Thunb.
Viburnum dentatum Lo

 

mid to late Hibiscus syriacus L.,
all season Indigofera potanini Craibo
Autumn early to mid Clematis paniculata Thunb°

mid autumn to
early winter Hamamelis virginiana Lo

 

Winter late winter to
early spring Hamamelis vernalis Sarge

Specimen plants were selected at various permanent locations on
the campus of Michigan State University (latitude 42047' N, longitude
84036' W) to supply sufficient samples over a 2 year perioda Since
mature plants of large size or a large group of less mature plants in
1 location were required to supply a sufficiently large number of col—
lections some variations in the environmental conditions of shade,

exposure, soil, and irrigation were necessary“

19

 

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20

Collections of both vegetative and reproductive buds were made at
frequent intervals. During 1962, collections of buds were made at
approximately the same time of day every 14 days starting on March 3
and ending October 27.

During 1963 collections of buds were taken more frequently.
Samples from the winter, spring and summer groups were collected
every other day from March 1 until the flower buds were visible and fully
swollen. The autumn flowering specimens were collected every 7 to 10
days until growth was rapid at which time samples were taken every other
day until late summer. From the time the flower buds were visible and
clearly identifiable, samples were collected less frequently-~5 to 7 days
apart.

From early November, 1963 until early April 1964 collections were
made at 3 to 4 week intervals. Collections were terminated at the end of
April, 1964.

For the purposes of this investigation, the time of flower initiation
was considered to be that time at which the meristem was observed to be
somewhat elongated and showed a definite broadening and flattening of
the buttress. Differentiation was considered to start when the first pro-
tuberances were noticed emerging from the buttress surface. When the
flower was completely formed in the bud, differentiation was considered
to be ended.

After collection each bud specimen was trimmed of excess parts,
placed in a 2 Ounce bottle containing formalin-acetic acid--70 percent
alcohol (FAA) solution and evacuated in an aspirator for at least 12 hours,
and stored in FAA.

During 1962 the alcohol—chloroform (with Eosin B added to the 70
percent alcohol solution) dehydration series was used exclusively. Dur—
ing 1963 and 1964 the tertiary butyl alcohol (TBA) dehydration series

was substituted to save time with the larger number of samples needed.

21

Eosin B was added to the 70 percent TBA solution to aid in ease of place-
ment of the specimens in the paraffin blocks, and a 35 percent and 70
percent TBA-paraffin oil solution were substituted for the 50 percent
paraffin oil solution. Embedding was accomplished in 560 C. (i l0 C.)
”Tissuemat“ paraffin.

In order to facilitate sectioning, buds were placed in a softening
solution (2:1 70 percent alcohol-glycerin solution) for about 1%— weeks.
Since dormant buds of Hamamelis vernalis Sarg. and Hamamelis
virginiana L. were still too hard for cutting another softening solution
containing 75 parts absolute alcohol, 15 parts glycerin and 20 parts
glacial acetic acid was employed for buds of these species. After this
treatment for 2 weeks these buds were sufficiently soft to be sectioned
without difficulty.

Microscopic sections were made on a rotary microtome 12 to 15
micra in thickness. Median sections were mounted on microscopic
slides and stained with Heidenhain's hematoxylin using ferric ammonium
sulfate (purple crystal) as the mordant. More than 7000 slides were
prepared and observed.

The following field observations of seasonal traits were recorded
for all plants: flowering dates, date of leaf expansion, date of fruit
maturation, fruit type and color, and the time vegetative growth began.
The first flowering date was considered to be the time the plant first
produced flowers. The final date was considered to be the date at
which 90 percent or more of the flowers had faded. The date of fruit
maturation was recorded when 90 percent of the fruit showed mature
color (Table 2). The date of leaf expansion was considered to be that
date on which the average length of 10 leaves-—in centimeters==fell
within the limits designated in Table 2. The date of vegetative growth
commencement was considered to be that date on which vegetative parts
could be seen with the naked eye pushing through the bud.

Field observations during 1962, 1963 and 1964 were recorded

3 times per week throughout the growing season.

 

 

 

 

 

 

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RESULTS

Clematis paniculata Thunb. (Ranunculaceae Juss.)

Gross Morphology: The period of vegetative growth began from
mid-April to early May from axillary buds near the crown of the plant.
Much of the previous season's growth of this vine died back without
harm to the plant. Vegetative growth continued at a rapid rate until
the end of June. At this time, a reduction in growth resulted from the
decrease in the length of the nodes accompanied by an increase in size
of the axillary buds. The normal vegetative growing point became a
long, slender tube with the nodes spaced further apart (Figure l-A).
Vegatative growth stopped entirely when the first flower buds became
visible in mid-July.

Flower formation began at the same time vegetative growth began
to decrease. Flower initiation became evident from mid to late July
with anthesis occurring between mid-August and early September.

The "king‘l flower of the panicle was the first to be initiated with the
others following in succession. The "king" flower was also the first to
open with others following rapidly. Flowering occurred acropetally on
current season's growth.

Fruits matured a week to a week and a half after flowering.

While the fruit was maturing on some flower receptacles other flowers

were developing to anthesis. Normally a small amount of flower develop-

ment occurred during the period of anthesis.

23

 

24

Table 3: Growth Characteristics of Clematis paniculata Thunb.

 

 

Vegetative Flower Bud Date of Days from
Growth Flowering First Visible lniti- Initiation to
Year Began Began Ended to Naked Eye ation Flowering
1962 5/5 8/15 10/19 7/10 6/26 40
1963 3/29 8/15 9/18 7/14 7/16 30
1064 4/16 8/27 7/17

 

Vegetative Apex: Before vegetative growth commenced in the
spring, the vegetative apex was a low, compressed primordial mass
with a rather shallow buttress (Figure l-B). As growth started the
growing point soon was high and dome-like (Figure l-C). Several pairs
of opposite primordial leaves were visible in the last half inch of the
growing point until floral appendages started to appear. The high domed
buttress presented a high degree of cell disorganization during growth.

An organized 2-celled tunica layer was visible, however.

Floral Apex: Floral primordia became evident about 30 days
before anthesis (Figure l—D). At this time, the petaloid sepals were
strongly visible enclosing a rather high primordial dome. The dome at
this time had begun to widen somewhat at the base. Approximately 5
days later protuberances were formed on this enlarged basal area
(Figure l-E). The high dome was still present as stamen primordia
were being laid down. Several cycles of stamens were initiated and
began growth. At the end of July the anthers began to expand and carpels
were initiated (Figure 1—F), and the high dome became non—existent.
The dome became the receptacle on which the achenes rested. Some
10 days later, locules in the carpels could be identified as well as ovule
development (Figure 1-G). By this stage the stamens had surmounted

the carpels. By late August the carpels and stamens were well developed

 

 

Figure l:

25

Stages in the development of flower buds in Clematis

mowepom

paniculata Thunb .

A.

Left - -vegetative bud.
Right—-flower buds a few days before anthesis.

. Vegetative apex during dormancy (approx. 35x).

. Vegetative apex after growth resumed (approx. 35x).

First indication of flower bud formation (approx. 45x).

. Stamen primordia laid down (approx. 45x).

Carpel initiation (approx. 25x).

. Flower a few days before anthesis (approx. 10x).

. Ovule development (approx. 18x).

'FET

26'

 

 

27

and microsporogenesis and megasporogenesis Were almost completed
(Figure l-H). Four to five days later anthesis occurred, first in the
"king" flower and progressed successively to each of the other flowerd
in the panicle.

Flower initiation occurred during mid-summer after approximately
60 days of vegetative growth. A high domed buttress enclosed by
petaloid sepals was apparent at first. By the end of July the stamens
were developing rapidly and the carpels were just beginning to form.
During August the carpels and stamens completed development with
anthesis occurring from late August to early September. Microsporo-
genesis and megasporogenesis seemed to be confined to the last 10 to

14 days of flower development.

Cornus mas L. (Cornaceae Lk. , Section macrocarpium Spach.)

Gross Morphology: Vegetative growth commenced in April after
flower anthesis and continued rapidly until the end of May. At this time
growth began to slow down as buds began to develop, but the flower and
vegetative buds were not distinguishable. Growth ceased altogether dur‘=
ing mid-June when flower buds became Visible. Both types of buds were
observed to enlarge through the summer. The flower buds at the time
of dormancy were approximately oneuquarter inch in diameter and the
vegetative buds about one-eighth inch in diameter in midchtober. Buds
passed the dormant season in this condition (Figure 2-A).

Floral growth became evident during late May or early June and
progressed rapidly until the end of August. At this time the floral parts
were complete but microsporogenesis and megasporogenesis had not
begun. The flower Over—wintered in this stage, completing development
with the commencement of growth the following spring. Anthesis

occurred in early April, 4 to 5 days before vegetative growth appeared.

28

The fruit matured in- mid-August, developing and reaching maturity

with the flower buds.

Tabley4; Growth Characteristics of Cornus mas L.

 

Days from

 

Vegetative Flower Bud Date of Inflorescent
Growth Flowering First Visible Initi- Initiation to
Year Began Began Ended to Naked Eye ation Flowering
1962 4/26 4/22 5/3 6/12 5/28
1963 4/6 4/2 4/24 6/12 5/27 309
1964 4/18 4/13 4/23 5/28 321

 

Vegetative Apex: The vegetative apex presented a shallow concave

surface with leaf primordia cut off in an opposite arrangement (Figure

2-B). The buttress consisted of a tunica at least 2 cells deep.

The

corpus appeared to have cells stacked in a modified tier arrangement.

As vegetative growth progressed and new leaf primordia Were cut off,

the buttress appeared to flatten out slightly (Figure 2—C).

Although this

feature was observed frequently it could not be associated only with floral

growth.

Floral Apex: The first indication of flower formation was a broad

and flattened buttressed surface (Figure 2-C) in late May.

The floral

apex at this time was observed to be somewhat wider than in a vegetative

apex which showed a flattened apex. Four to five days later the apex

surface presented a series of ridges which eventually developed into

florets (Figure 2-D). Each ridge—like primordial mass represented a

floret of the umbel. By mid—June the primordial mass developed into a

cup—shaped receptacle with sepal primordia present and a slight convex-

shaped surface (Figure Z—E). At the same time, or 2 or 3 days later,

 

Figure 2.

Stages in the development of flower buds in Cornus mas L.

A.

29

Vegetative bud, left.
Flower bud, right.

B. Vegetative apex (approx. 45x).

0

L'EQHIFJU

. First indication of inflorescence formation

(approx . 45x) .

. Floret initiation (approx. 35x).

. Sepal formation (approx. 35x).

. Petal primordia (approx. 30x).

. Stamen initiation (approx. 35x).

. Carpel and disk formation (approx. 30x).

. Antropous ovule and microsporogenesis

(approx. 25x) .

. Flower bud with the onset of dormancy

(approx. 10x).

hummus-3.1““? “ ‘ ’

30

 

31

petal primordia had emerged (Figure 2-F). By late June the stamen
primordia could be ascertained (Figure Z-G). Sepal elongation had
ceased, a carpel with a locule became visible, and a very small disk
was beginning to form (Figure 2—H) during the last 2 or 3 days in June;
the petals had lengthened, encircling the floret. Floral development
during July appeared to have decreased after rapid development during
June. Ovule development and microsporogenesis appeared to begin at
approximately the same time in mid to late July. By late July the
anatropous ovule was evident as was microsporogenesis (Figure 2-I).
The flower bud continued to expand until the time of dormancy, with
microsporogenesis being completed and the ovule developed to at least
the point of megasporogenesis (Figure 2-J). In early spring megasporo-
genesis apparently began at least 2 weeks before and was completed
several days before flowering. Some evidence was found, but could not
be substantiated, that megasporogenesis began in the late fall.

The inflorescence was initiated in late May with floret primordia
appearing 4 to 5 days later. Floret development occurred in acropetal
succession rather rapidly until early July. Carpels were evident in
early July, however, ovule development did not begin until mid to late
July. Ovule development and microsporogenesis appeared to begin at
appr0ximately the same time. When dormancy set in, microsporogenesis
had been completed. Megasporogenesis appeared to take place in early
spring, starting at least 2 weeks before anthesis. Anthesis occurred in

early to mid-April.

Forsythia ovata Nakai. (Oleaceae Lindl.)

Gross Morphology: Vegetative growth began during April and con-
tinued rather rapidly until the first of June, when growth began to

decrease until it completely stopped at the end of June. Buds became

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evident toward the end of May but were not distinguishable except by
position. Vegetative buds were produced in the axils of leaves and at
the apex of the new shoot (Figure 3-A). In many cases vegetative buds
were not observed in axils of the 2 most proximal leaves.

Flower buds became clearly evident by the end of June toward the
base of the current season‘s growth. Flower buds were often situated
in the axils of the 2 most proximal leaves. Development of flower buds
continued through the summer and by the end of October these buds
were approximately twice as large as the vegetative buds. The flower
buds were commonly in a multiple collateral arrangement (Figure 3-A).

Fruit development started soon after flowering and was evident
through the summer. The tear-drop shaped fruit matured in late

September to early October.

Table 5; Growth Characteristics of Forsythia ovata Nakai.

 

 

Vegetative Flower Buds Date of Days from
Growth Flowering First Visible Initi- Initiation to
Year Began Began Ended to Naked Eye ation Flowering
1962 4/26 4/21 4/30 5/12 6/10
1963 4/3 4/2 4/25 5/11 5/20 296
1964 4/17 4/12 4/25 5/14 328

 

Vegetative Apex: The vegetative apex appeared as a rather high
concave buttress with leaf primordia cut off in an opposite arrangement
(Figure 3—B). The tunica consisted of 2 highly organized cell layers and
1 cell layer not as highly organized. The corpus was about 5 to 7 cells
deep with the upper cells apparently part of the third cell layer of the

tunica.

'-'.ru1r‘ ream]! .

 

in mud . I

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33

Floral Apex: The first indication of flower formation became
apparent in mid-June when the surface was flat across the top of a
raised buttress (Figure 3-C). Sepal primordia appeared a few days
later surrounding a concave buttress which was shallow (Figure 3-D).
By the end of June the buttress surface was much IOWer in outline
(Figure 3-E) with petal primordia evident in early July (Figure 3-F).
Stamen primordia were evident by mid—July and by the end of July
(or occasionally August), the carpel and a locule were present (Figure
3-G). Ovule formation was observed in mid-=August (Figure 3-H) at
the time of microsporogenesis, when the carpel had elongated consider-
ably displaying the 2—lobed stigma of the style. The flower bud con-
tinued to expand until mid-September when the anatropous ovule was
distinct and mic rosporogenesis appeared to have been completed
(Figure 3-1). At this time the microstyle was evident with a short 2w
lobed stigma and 2-loculed ovary. The flower bud was approximately
three-quarters of an inch in length and quite plump. The bud over—
wintered in this stage and completed development the following spring
when megasporogenesis commenced approximately 2 weeks before
anthesis.

The floral apex was slightly concave until the petal primordia were
formed. Floral parts initiated in an acropetal succession beginning
during mid-June. Ovule formation and microsporogenesis were evident
during mid-August and were completed by the end of September.
Megasporogenesis was not observed until approximately 2 weeks before

anthesis. Anthesis took place from early to mid-April.

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Figure 3:

34

Stages of development in flower buds of Forsythia ovata Nakai.

A. Vegetative (left) and flower buds (right).

B. Vegetative apex (approx. 45x).

C. First appearance of flora structures (approx. 45x).
D. Sepal primordia (approx. 45x).

E. Stage just before petal initiation (approx. 45x).

F. Petal formation (approx. 40x).

G. Stamen primordia, carpel and locule (approx. 30x).
I-l. Ovule formation (approx. 30x).

1. Flower bud as it over-wintered (approx. 10x).

35

 

A

 

 

36

Hamamelis vernalis Sarg. (Hamamelidacea Lindl.)

Gross Morphology: Vegetative growth began in mid-April 1 to 3
days after flowering had occurred. Shoot and leaf growth continued
rapidly until mid to late June at which time flower buds were distinguish-
able. Stem growth was observed to average approximately 6 to 8 inches
during the period of greatest activity. Vegetative growth began to
decrease in length during mid-June and had ceased completely by mid-
July.

Floral bud clusters became evident from mid to late June. They
appeared as a small rounded mass of tissue surmounting a peduncle
about one-quarter inch long. As the season progressed, the size of the
cluster mass continued to increase until the individual flowers could
clearly be distinguished by mid to late July (Figure 4—A). The flower
clusters were observed to contain 1, 2, or 3 flowers and very rarely
4 flowers. The individual flowers continued to develop and swell until
dormancy at which time they were approximately one=eighth inch in
diameter. The buds remained in this condition over—winter and anthesis
took place in mid-March the following year. All flowers were produced
on the previous season's wood.

Fruit development started soon after the flowers wilted and con-
tinued throughout the summer. The woody capsule matured in early to

mid-October of the same year of anthesis.

Table 6: Growth Characteristics of Hamamelis vernalis Sarg.

 

 

Vegetative Flower Buds Date of Days from
Growth - . Flowering First Visible Initi== Initiation to
Year Began Began Ended to Naked Eye ation Flowering
1962 4/14 3/17 4/14 6/19 6/10
1963 4/18 3/18 4/18 6/12 6/3 281

1964 4/18 3/2 4/14 5/28 273

 

    

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37

Vegetative Apex: The vegetative apex was observed to consist of
a rather high concave, evenly rounded surface with leaf primordia cut
off alternately (Figure 4-B). A 1-celled tunica was present with a highly
disorganized 10 cell deep corpus beneath the tunica. Vegetative apices,
in general, were axillary with the exception of the terminal point for

approximately 4 inches proximal to the terminal.

Floral Apex: Flower initiation began in late May to mid-June.
At this time the floral apex showed a central pyramidal column of tissue,
sloping, gradually to the bracts which surrounded the apex (Figure 4—C).
The tissue between the bracts and column was highly meristematic and by
late May had flattened out considerably (Figure 4-D). The surface of the
flattened area also showed a slight protuberance which later developed , ,1
into a flower. The outer bracts at this time had elongated some and
covered the flower cluster. In early June the bracts of the individual
flowers became visible (Figure 4—C). Also visible at this time was a
slight concave surface on the concave buttress surface with the first
evidence of the sepals (Figure 4—F). The petals became evident from
early to mid—July (Figure 4-G). The stamens arose simultaneously or
soon after the petals. At the same time very small carpel primordia
were present. In early August, the carpel was well—developed including
the presence of a locule (Figure 4=H). Ovule formation and micro—
sporogenesis were not observed. Ovules, however, were formed from
late August to early September (Figure 4-1). Microsporogenesis had
begun at this time also. Pollen grains were completely formed at the
time of dormancy (Figure 4-J). Most ovules remained undifferentiated
throughout the winter with megasporogenesis starting 5 0t 6 days before
anthesis. Anthesis occurred in mid to late March.

Flower initiation began in early June approximately 45 days after
vegetative growth began. The individual flowers in the cluster became

Visible in early June. The sepals, petals, stamens and staminoids, and

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Figure 4: Stages of development of the flower buds .in- Hana-111% _' ' 5'-’;_.:.": :
vernalis Sarg. and I-_I. virginiana L. '-

. A .

Vegetative bud, right

~ Flower bud, left.

o~

uHmofiimoow

Vegetative apex- (approx. 35x).

Floral apex (approx. 35x).

. Prirnordia of inflorescence (approx. 35x).

.. Bracts of flowers and flattened buttress (approx., 30):).
. Appearance of sepal primordia (approx. 40x).

. Petal primordia (approx. 40x).

. Carpel with locule (approx. 40x).

. Ovule formation (approx. 20x).

. Flower at the onset of dormancy or before anthesis

(approx. 10x).

 

 

40

carpels arose in acropetal succession throughout the summer. Ovule
formation became evident during early September at the time micro-
sporogenesis began. Microsporogenesis was completed by the time
dormancy began. Ovule development and megasporogenesis were com—
pleted the following March. Megasporogenesis was observed to start
in early March and complete development a few days before anthesis in

mid to late March.

Hamamelis virginiana L. (Hamamelidaceae Lindl.)

 

Gross Morphology: Vegetative growth commenced 2 to 10 days
later than in Hamamelis vernalis Sarg. By mid-June growth had caught
up to the same stage as in 11. vernalis Sarg. and continued to show
similar stages throughout the remainder of the season (Figure 4-A).

In general, vegetative growth was less rapid or achieved less length
growth than E. vernalis Sarg.

Floral bud clusters became evident during mid-June and continued
development as in I-_1. vernalis Sarg. Flowers buds were approximately
one—half the size of those in El vernalis Sarg. (Figure 4—A). Individual
flower buds were about one—sixteenth inch in diameter when anthesis
occurred in early to mid—October.

Fruit development did not start until growth resumed the next
spring and proceeded until maturity the same autumn. The woody cap-

sule matured in early to mid—October.

Table 7: Growth Characteristics of Hamamelis virginiana L.

 

 

 

Vegetative Flower Buds Date of Days from

Growth Flowering First Visible Initi- Initiation to
Year Began Began Ended to Naked Eye tion Flowering
1962 4/28 10/16 12/9 6/14 5/25 144
1963 4/20 10/20 12/7 6/12 5/30 143

1964 4/28 6/4

 

    

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41

Vegetative Apex: Similar to Hamamelis vernalis Sarg. (Figure
4-B).

Floral Apex: Although similar to Hamamelis vernalis Sarg.

, (Figure 4-C, D, E, F, G. H, I, and J), flower initiation commenced

4 to 15 days earlier. Individual floral parts appeared in acropetal
succession and within a few days of those in buds of Hamamelis vernalis
Sarg. Microsporogenesis and megasporogenesis started at least 1 month
later, toward the end of September, and were completed a day or 2 be-
fore anthesis in mid-October.

Flower initiation began in late May or very early June. Flower
part formation and development were observed to be similar to
Hamamelis vernalis Sarg. Microsporogenesis and megasporogenesis
began toward the end of September and were completed a day or 2 before
anthesis. Anthesis occurred in mid-October and continued until the

flowers were killed by freezing in early December.

Hibiscus syriacus L. (Malvaceae Zeck.)

Ere—5s Morphology: Vegetative growth commenced from buds
embedded beneath leaf scars (Figure 5—A) in mid-spring and continued
until appr0ximately mid-August. Approximately 30 days after vege-
tative growth began the first small flower bud could be seen in a leaf
axil 2 or 3 inches up the shoot. Stern and leaf growth continued until
all flower buds were formed and the 2 or 3 most proximal buds had
bloomed. At this point vegetative growth had stopped completely.

Flower buds were formed in acropetal succession starting in
early to mid-June. Flowering, also in acropetal succession, commenced
during July or early August. The buds at this time were about one—half
inch in diameter and 1 inch long. Flower bud formation was observed

to proceed while anthesis was taking place further down the stem.

    

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Conversely, fruit development was proceeding while the upper flower
buds were open or developing to anthesis.

Fruit develOpment rapidly followed anthesis with the first capsules
dehiscent during early October. All fruit had dehisced by mid-November.
The capsule persisted into the fall of the year following. Seed was dis—

persed throughout the winter.

Table 8: Growth Characteristics of Hibiscus syriacus L.

 

 

Vegetative Flower Buds Date of Days from
Growth Flowering First Visible Initi— Initiation to
Year Began Began Ended to Naked Eye ation Flowering
1962 5/1 8/6 9/6 6/19 6/1 66
1963 4/18 7/20 9/14 6/3 5/22 59
1964 4/23 7/6 9/2 5/26

 

Vegetative Apex: The vegetative growing point presented a shallow
concave surface with leaf primordia cut off in an alternate arrangement
(Figure 5-B). The tunica consisted of a single highly organized cell
layer and perhaps a second layer which was not as highly organized.
Beneath the tunica layer was a central corpus of disorganized cells 5 to

6 cells in depth.

Floral Apex: The first indication of floral initiation was a flattened
apex of an axillary bud (Figure 5—C) in early to mid-May. Several bracts
of the involucre which surround the flower bud were also visible at this
time. Toward the end of May the peduncle of the flower bud had elongated
to about 3 mm in length and sepals were evident (Figure 5-D). At this
time, the buttressed apex had assumed a shallow concave surface and

became flattened. The floral apex presented a surface much like that of

 

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43

the vegetative apex. Within 1 or 2 days this apex showed 2 primordial
masses rising to either side with the flattened central surface remain-
ing flat (Figure 5-E). On the outer portion of these larger primordial
masses was a single smaller vesture which developed into juvenile
petals; the larger masses in the vesture became the young staminal
column. During early June protuberances of the staminal column con-
tinued to develop at a faster rate than the petal primordia (Figure 5-F)
and the central part of the buttress remained flattened. By mid-June,
however, the staminal column enclosed a cavity which contained several
carpels with locules (Figure 5—G). The petals were now almost as long
as the staminal column and stamen primordia could be distinguished.
The styles of the carpels were observed to be separate and just starting
to elongate. Flower buds continued to develop rapidly until the staminal
column filled the bud (Figure 5—1-1) toward the end of June. The bud at
this time was approximately one-quarter inch long. The petals had
surmounted the staminal column, recurved to a certain extent, with the
style branches almost grown through it. Ovule development and micro-
sporogenesis commenced from mid to late June (Figure 5-1). The style
branches had grown completely through the staminal column by early

to mid-July (Figure 5-J). Microsporogenesis had been completed

and megasporogenesis had just begun. Within 4 or 5 days the buds began
to open.

As the buds opened, the petals were observed to be convolute and
to remain tight until they extended to a length of approximately 4 inches.
During this time the staminal column also elongated to approximately
the same length and the style branches had elongated to 1 inch above the
stamens. Megasporogenesis continued and was completed when the petals
opened. From the time that the petals emerged until petal anthesis
occurred 4 to 8 days had passed. Anthesis normally occurred from

early July to early August.

 

'.' ._.- n'J ”flil-‘lfla

 

44

Figure 5‘. Phases of flower bud development in Hibiscus syriacus L.
A. Leaf scar and stem.
B. Vegetative apex (approx. 30x).

C. Flower initiation showing involucer bracts
(approx. 40x).

D. Elongated flower bud with sepal primordia
(approx. 40x).

E. Staminal column and small petal primordia
(approx. 30x).

F. Growth of petal and staminal column primordia
(approx. 30x).

G. Carpel primordia with locules (approx. 15x).
. Petal and staminal column elongation (approx. 15x).

1 . Ovule and microsporogenesis initiation
(approx. 15x).

J . Flower 3 or 4 days before anthesis (approx. 4x).

45

 

 

46

Flower bud development was a modified acropetal succession.
Involucre bracts and sepals were formed from the middle to the end
of May. In early June a primordial mass arose, containing both
staminal column and slightly later the petals. Undifferentiated stamen
primordia and carpel primordia appeared to arise simultaneously during
mid—June. Locules were evident a few days later. Ovule development
and microsporogenesis occurred toward the end of June. Megasporo-
genesis began approximately 3 to 4 days before petal emergence. The
petals, staminal column, style and megasporogenesis completed
development from early to mid—June with anthesis following. Flower

buds formed ac ropetally.

Indigofera potanini Craib. (Leguminosae B. Juss.,
Subfamily Lotoideae)

Gross Morphology: Vegetative growth and flower bud develop—
ment both began in mid-spring and continued until mid-August. As
growth ceased, buds ceased pushing out primordial leaves and began
to produce bracts. In the axil of each bract "embryo" racemes formed
and over-wintered. By the end of October buds were one—quarter inch
in length, about one-eighth inch in width, and contained miniature
racemes, leaf and other vegetative structures (Figure 6cA).

Flower inflorescence initiation and development resumed when
vegetative growth commenced in the spring. The first raceme became
evident to the naked eye approximately 16 days before anthesis.
Racemes continued to be initiated through the summer and up to the
time of dormancy. During the winter some of these highly undifferentiated
meristematic racemes were killed by low temperatures but others sur-
vived to develop to anthesis the next spring. The flowering period ex—
tended through the entire summer and into mid or late September.

Racemes and flowers developed in acropetal succession with anthesis

 

 

.' : ' ‘.“'.-EMIL-

 

47

occurring in the proximal flowers while the distal flowers were still
developing (Figure 6-A). Flower parts appeared to be formed in acro-
petal succession.

Small fruits were first evident toward the last of July and maturity
was reached in early to mid-October. The fruit often persisted until

early March.

Table 9: Growth Characteristics of Indigofera potanini Craib.

 

 

 

Vegetative Flower Raceme Date of Days from

Growth Flowering First Visible Initi- Initiation to
Year Began Began Ended to Naked Eye ation FlowerinL
1962 5/1 5/22 9/30 5/10 Continuous Continuous
1963 4/18 6/3 9/16 5/19 from growth from growth
1964 4/28 5/19 5/3 resumption resumption

to dormancy to dormancy

 

Vegetative Apex: The vegetative apex presented a rather shallow
domed apex with leaf primordia cut off alternately (Figure 6-B). The
tunica contained 3 layers of organized cells and a corpus 3 or 4 cells

deep. The corpus appeared to be somewhat organized.

Floral Apex: The first indication of floral initiation was evident
from the development of an apex similar to the vegetative apex with
primordia in axils just below the apex (Figure 6=-C). The floral apex
at this time was flattened on the shoulder and raised in the center.
Within 10 days the inflorescence had expanded exposing many more
flowers in the raceme (Figure 6—D). Sepals appeared to have been
initiated in the proximal flowers in the inflorescence. The raceme con»
tinued to expand in length cutting off bracts and flower primordia as it

elongated (Figure 6-E) with the small raceme still enclosed by a bract

 

48

and invisible to the naked eye. The above 3 stages were observed in
over-wintering multiple buds.

The first actual differentiation was not observed until approxi-
mately 7 days after vegetative growth had started when several stages
of development could be observed. The proximal flowers of the raceme
appeared to have all floral parts present (Figure 6-F). Approximately
10 days after the raceme became visible in early to mid-May, anthesis
started and proceeded over a period of 3 to 4 months.

As vegetative growth began individual flower formation resumed
growth. The flower primordia at first presented a rather high domed
primordial mass, always axillary until the terminal primordia differ—
entiated (Figure 6—F). The buttress appeared to flatten across the top
and at the same time primordial masses were cut off on the side
(Figure 6—G). Petal primordia were cut off to the sides of the domed
primordial mass just inside the sepals. Stamens apparently formed
simultaneously or slightly later than the petals. As the raceme began
to emerge and become visible, ovule development and microsporogenesis
became evident (Figure 6—1-1). By this time the racemes were one-half
inch long, the ovules in the lowerumost flowers were well formed and
microsporogenesis was approximately half completed (Figure 6—1).
From the first appearance of the racemes to anthesis required approxi—
mately 10 to 15 days during which microsporogenesis was completed;
megasporogenesis began and finished during the same period. Anthesis
took place between late May and early June and continued into mid=
September or late September. The greatest amount of flowering occurred
in the first 4 to 5 weeks. The rest of the season flowering gradually
decreased until the end of September.

Flower racemes were shown to over==winter in a highly undifferw
entiated state; in some cases, sepals and petals were barely visible.

While the acropetal order of succession appeared to be usual the petals,

.l
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Figure. 6:

Flower bud development in Indigofera. potanini Craibl

A. Dormant mixed buds (arrow).

. B. Vegetative apex- (approx. 40x).

C. Raceme primordia mostly undifferentiated
(approx. 40x)

D. Raceme with some flower differentiated in the
proximal flowers (approx. 40x).

F1

. Raceme elongating with some flower differentiation
(approx. 40x).

. Floral parts; sepals (approx. 20x).
. Sepals, petals, stamens (approx. 20x).

. Ovule and microsporogenesis initiation (approx. 10x).

”$091

. Flowers several days before anthesis (approx. 55x).

 

50

 

 

51

stamens and carpel often seemed to initiate and develop at the same
time. Ovule and microsporogenesis Were initiated as the raceme

first became visible to the naked eye. The ovules were well formed

at the time the raceme was one-half inch long. In the 10 to 15 days
before anthesis, microsporogenesis was completed and megasporo—
genesis was initiated and completed development. Anthesis first
occurred in mid-May to early June and continued until mid—September.
Vegetative growth, floral initiation and development, and fruit develop-

ment were shown to proceed simultaneously throughout the summer.

Prunus glandulosa Thunb. (Rosaceae Juss.,
Subfamily Prunoideae Focke.)

Gross Morphology: In mid—spring vegetative growth started and
continued until the end of July. In mideuly buds were observed in
leaf axils but were not distinguishable between flower and vegetative
buds. During the remainder of the summer the buds increased in size
and by mid==September the collateral bud arrangement became visible
(Figure 7=A).

Flower buds were present by mid=September and continued to
enlarge until dormancy. At the time of dormancy the collateral bud
arrangement was clearly visible with the vegetative bud surrounded by
floral buds.

Flower development began during late August or early September.
By the last of October all flower parts were almost fully developed.
With the commencement of growth the following spring the stamens and
carpels completed development and microsporogenesis and megasporo-
genesis started approximately 10 days before anthesis. Anthesis
occurred in late April or early May.

Fruits developed to maturity during the first half of the summer

reaching maturity from mid to late July.

 

51

stamens and carpel often seemed to initiate and develop at the same
time. Ovule and microsporogenesis were initiated as the raceme

first became visible to the naked eye. The ovules were well formed

at the time the raceme was one—half inch long. In the 10 to 15 days
before anthesis, microsporogenesis was completed and megasporo=
genesis was initiated and completed development. Anthesis first
occurred in mid—May to early June and continued until mid-September.
Vegetative growth, floral initiation and development, and fruit develop-

ment were shOWn to proceed simultaneously throughout the summer.

Prunus glandulosa Thunb. (Rosaceae Juss. , ‘
Subfamily Prunoideae Focke.) _

 

Gross Morphology: In mid-spring vegetative growth started and
continued until the end of July. In mid-July buds were observed in
leaf axils but were not distinguishable between flower and vegetative
buds. During the remainder of the summer the buds increased in size
and by mid=September the collateral bud arrangement became visible
(Figure 7=A).

Flower buds were present by mid=September and continued to
enlarge until dormancy. At the time of dormancy the collateral bud
arrangement was clearly visible with the vegetative bud surrounded by
floral buds.

Flower development began during late August or early September.
By the last of October all flower parts were almost fully developed.
With the commencement of growth the following spring the stamens and
carpels completed development and mic rosporogenesis and megasporo-
genesis started approximately 10 days before anthesis. Anthesis
occurred in late April or early May.

Fruits developed to maturity during the first half of the summer

reaching maturity from mid to late July.

 

52.

Table 10: Growth Characteristics of Prunus glandulosa Thunb.

 

 

Vegetative Flower Bud Date of Days from
Growth Flowering First Visible Initi— Initiation to
Year Began Began Ended to Naked Eye ation Flowerig
1962 4/24 5/1 5/16 9/30 8/18
1963 4/20 4/28 5/13 9/18 8/21 252
1964 4/19 5/1 5/9 253

 

Vegetative Apex: The vegetative apex presented a concave, high
domed buttress with leaf primordia cut off alternately (Figure 7= B).
The tunica was at least 2 layers deep and perhaps 3. The corpus was

highly disorganized and approximately 5 cells deep.

Floral Apex: The first indication of flower primordia appeared
in mid=August in the form of rounded primordial masses slightly flattened
across the top (Figure 7mC). Ten days later the buttress had broadened=
out and the shoulders of the buttress had flattened (Figure 7=D). Sepal
primordia became evident by the end of August (Figure 7=E). Rapid
development followed with petal and stamen primordia usually appearing
simultaneously or occasionally the stamens very slightly thereafter.
By mid-September the carpels were distinguishable (Figure 7=F). The
perigynous flower became evident toward the end of September as the
style began to elongate (Figure 7=G). The flower bud normally overs
wintered in either the above condition or after ovule initiation. Ovules
which formed in the autumn were evident during midoOctober and at the
same time microsporogenesis was observed to have begun (Figure 7=H).
In most flowers ovule formation. as well as microsporogenesis, was
initiated during early spring. The ovule was well formed by mid=April

and microsporogenesis was mostly complete (Figure 7=-I).

 

- PO:

 

 

Figure 7:

53

Stages in the development of flower buds of Prunus

glandulosa Thunb.

A. Collateral multiple buds (vegetative bud central).

B. Vegetative apex (approx. 40x).

C. Flower primordia appearance (approx. 40x).

D. Buttress surface ready for differentiation
(approx. 40x).

E. Sepal primordia (approx. 40x).

F. Sepal, petal, stamen and carpel primordia

(approx. 60x).
G. Perigynous flower evident (approx. 40x).

H. Ovule and microsporogenesis initiation
(approx. 15x).

[-4

. Flower bud when growth resumed the following
spring (approx. 15x).

J . Flower several days before anthesis (approx. 15x).

54

 

 

55

Megasporogenesis was not observed at this time. The anatropous ovule
was visible approximately 10 to 15 days before anthesis while mega-
sporogenesis occurred during this time (Figure 7-J). Anthesis began
from late April and continued to mid-May.

Flower initiation occurred in acropetal succession starting in mid-
August. Sepals, petals, stamens and carpels were well—developed at
dormancy. Ovule formation was observed to begin either in mid-=October
or, in most cases, when growth resumed the next spring. Microsporo—
genesis started approximately at the time ovule initiation was observed.
Megasporogenesis began 10 to 15 days prior to anthesis. Anthesis

occurred from late April to mid—May.

Pyracantha coccinea Roem. var. lalandii Dipp.
(Rosaceae Juss., Subfamily Promiodeae Focke)

 

Gross Morphology: Active vegetative growth began during April
and continued until the end of August or early September. Buds became
visible during mid—June but no distinction could be made between
reproductive or vegetative buds at this time. By the end of August, the
respective buds could be identified and by mid=September they were both
clearly visible (Figure 8wA). As the autumn progressed the flower buds
were observed to swell until the end of October after which the buds
showed no change until growth resumed the next spring.

The inflorescence primordia became evident during late October
but remained in a highly meristematic state through the winter. When
vegetative growth commenced the next spring, this primordial mass
began to expand very rapidly. Flowers were initiated and developed to
anthesis during approximately 55 days. Flowers were borne on current
season' 5 wood.

Fruit development proceeded through the summer months, finally
maturing in early to mid=September. The fruit was found to persist

until the following February or March.

56

The leaves remained on the plants thr0ugh the winter with 75

percent abscission in February or March of the following year.

Table 11: Growth Characteristics of Pyracantha coccinea Roem. var.
lalandii Dipp.

 

Days from

 

Vegetative Buds First Date of Inflorescence
Growth Flowering Visible to Initi‘= Initiation to
Year Began Began Ended Naked Eye ation Flowering
1962 4/28 5/27 6/14 5/10 Inflorescence
lO/ZO, Flower
4/28
1963 4/6 5/31 6/12 5/7 Inflorescence 221
10/21, Flower
4/18
1964 4/18 5/24 6/9 5/1 214

 

Vegetative Apex: The vegetative apex was observed to be a high
concave buttress with a shallow curved surface (Figure 8wB). Leaf
primordia were cut off on the flanks in an alternate arrangement.

A tunica 2 cells deep was observed with a somewhat disorganized corpus

approximately 5 cells deep.

Floral Apex: The primordia of the corymb inflorescence became
visible in late October (Figure 8=C). At this time the apex within the
floral bud was highly meristematic with little differentiation into a
recognizable inflorescence, at which stage the flower bud over=wintered.

About the time vegetative growth resumed in the spring, individual
flower initiation became evident. The first indication was a definite
flattening of the meristematic buttress (Figure 8=D). Sepals became
apparent 10 days later in the uppermost flower of the corymb (Figure

8-E). Flower parts were formed in acropetal succession with the petals

 

 

 

Figure 8:

57

The development of floral buds in Py_racantha coccinea
Roem. lalandii Dipp.

EOWMUOW>

(fin-c

 

. Vegetative (upper) and flower buds (lower).

. Vegetative apex (approx. 40x).

. Inflorescence initiation (approx. 40x).

. Individual flower primordia appearance (approx. 40x).
. Sepal primordia (approx. 40x).

. Petal primordia (approx. 40x).

. Stamen and carpel primordia (approx. 40x).

. Carpel development in late spring (approx. 40x).

. Ovule and microsporogenesis initiation (approx. 30x).

. Microsporogenesis complete, megasporogenesis

starting (approx. 20x) .

58

 

 

59 -

appearing about 9 days later (Figure 8-F), stamens formed with the
petals or very quickly afterward, and the carpel primordia was evident
by the last of April (Figure 8—G). At the time the sepals first appeared
(Figure 8-E) the buttress surface was still flat. The buttress surface
changed to a shallow convex surface when the petals and stamens were
initiated (Figure 8-F). As the carpel primordia appeared, the buttress
surface again became flat (Figure 8-G) but during carpel development
this flattened area disappeared entirely (Figure 8-H, I).

Ovule initiation became visible in mid-May. At this time, all
flower parts were developed but microsporogenesis and megasporogenesis
had not yet begun. However, 1 or 2 days later, the first sign of micro—
sporogenesis and megasporogenesis became evident. By late May both
microsporogenesis and megasporogenesis were completed and the
flower was ready to open (Figure 8-J). Anthesis occurred in late May.

The first evidence of flower formation began in late October when
inflorescence primordia were seen. Over=winter, this primordium
remained in a highly undifferentiated state and began to expand as vege-
tative growth resumed the following spring. Sepals were initiated 10
days later, and carpels approximately 3 days later. By early May, all
flower part primordia were present. Ovule initiation was evident in
Mid-May with microsporogenesis and megasporogenesis limited to the

latter half of May. Anthesis occurred in very late May.

Rosa multiflora Thunb. (Rosaceae Juss.,
Subfamily Rosoideae Focke.)

 

Gross Morphology: With the commencement of vegetative growth
in early April, growth was rapid until mid to late May. During midaMay
growth began to decrease as the flowers emerged from the bud. Growth

had ceased by the last of May, 5 to 8 days before flower anthesis.

      

4‘ i

,, .’ ”‘.“ ,..
-"-:!l-.v1é' 1:, .1: b!

.; "1 Mutual

'.z‘e'wr‘

60

Vegetative buds were first visible in early July and continued to enlarge

until dormancy. Over wintering buds were vegetative only (Figure 9-A).
Floral development began 10 days after vegetative growth.

Flowers were initiated and developed during active vegetative growth.

Anthesis began in early June on current season's vegetative growth.
Fruit development occurred through the summer reaching maturity

during early Septembe r .

Table 12: Growth Characteristics of Rosa multiflora Thunb.

 

 

Vegetative Flower Bud Date of Days from
Growth Flowering First Visible Initi— Initiation to
Year Began Began Ended to Naked Eye ation Flowering
1962 4/4 6/1 6/28 5/15 4/28 33
1963 3/31 6/7 6/19 5/16 4/18 49
1964 4/14 6/4 6/20 5/14

 

Vegetative Apex: The vegetative apex appeared to be flat with a
slight concave surface. The cells of this region were highly disorganized
so that a definite tunica and corpus were not distinguishable. Leaf
primordia arose on the flanks of the buttress in an alternate fashion

(Figure 9-B).

Floral Apex: The individual flower primordia became evident 6 to
10 days after the commencement of vegetative growth. The buttress of
these primordial masses was highly concave in shape with leaf primordia
as well as flower primordia being cut off on the flanks of the terminal
primordia mass (Figure 9-C and D). The miniature corymb and flower
primordial continued rapid development until the buttress started to

flatten out approximately 18 to 30 days after vegetative growth began

I"A '
II I '
I

- '.- "'.‘:l 35ml]! - . ‘i

    

61

(Figure 9-E). At this time the flowering stern began elongating more
rapidly but was not observed outside of the enclosing immatured leaves.

Several days later at the time of the appearance of flower initiation
the buttress was a very shallow convex surface enclosed with very small
sepals (Figure 9-F). First, most terminal flower began development
followed by further flower development in an acropetal fashion. By the
end of April petal primordia appeared as small swellings just below the
developing sepal primordia (Figure 9-G). During the early part of May
the stamens were initiated. Ten days after petal development began, the
first signs of carpel formation were evident (Figure 9-H). At this time,
the stamens were somewhat higher, slightly overhanging the carpel
primordia, and the flower buds were beginning to become visible to the
naked eye.

In mid—May a definite epigynous flower could be recognized
(Figure 9—1). Both the sepals and petals were well developed but the
stamen and carpel primordia were still strongly meristematic. Carpel
primordia were observed to nearly triple in height in a matter of 8 or
9 days.

Ovule development was observed during late May (Figure 9=J) at
a time when the corymb was expanding rapidly and all flower buds were
visible.

Two or three days before anthesis in early June, microsporo=
genesis and megasporogenesis were completed (Figure 9=K). By this
time, the styles were observed to have grown through the open area
formed by the basal tissue of the sepals, petals and stamens. All flower
parts were initiated during the period of the most active vegetative
growth and in acropetal succession. Sepals were initiated approximately
20 days after vegetative growth started. Petals and stamens were

initiated 8 to 10 days later with the carpel primordia evident by mid—May.

 

 

- Figure 9: Development of flower buds .in' Rosa multiflora TB in?

A. Vegetative buds .

, B. Vegetative apex (approx. 35x).

Inflorescence primordia, early stage (approx.. 30x).
Inflorescence primordia, late stage (approx. 30x).
Individual flower buttress flattening (approx. 30x).
Sepal primordia (approx. 70x).

Petal initiation (approx. 50x).

.5392“???

Stamens present, carpel primordia (approx. 50x).

H

. Epigynous flower with developing carpels
(approx. 40x).

c_.

. Ovule development (approx. 15x).

K. Flower 1 to 2 days before anthesis (approx. 10x).

63

   

64

Microsporogenesis and megasporogenesis did not become evident until
10 to 12 days before anthesis. The inflorescence and flower parts

developed in acropetal succession.

Spiraea thunbergi Sieb. (Rosaceae Juss. ,
Subfamily Spiraeoideae Focke.)

Gross Morphology: Vegetative growth began at the time of flower
anthesis or slightly after anthe sis. Growth continued to expand rapidly
until mid-August at which time flower and vegetative buds were dis-
tinguishable (Figure lO—A). The small, slender stems tended to die
back quite a little during the winter months, especially the terminal 3 or
4 inches.

During the latter part of August floral buds can be distinguished
by being round and blunt at the apex (Figure lO—A). The flowers were
initiated and developed up to microsporogenesis and megasporogenesis
before dormancy. Some flowers developed to anthesis during early to
mid-October depending upon existing weather conditions. In general,
microsporogenesis and megasporogenesis were initiated and completed
after growth had resumed the following spring. Flowers were borne on
previous season's wood and were usually produced over a period of l or
2 months.

Fruit maturity was reached in late May or early June when the

follicles split open and dispersed the seed.

Table 13: Growth Characteristics of Spiraea thunbergi Sieb.

 

 

 

Vegetative Flower Bud Date of Days from
Growth Flowering First Visible lniti= Initiation to
Year Began Began Ended to Naked Eye ation Flowering
1962 4/24 4/27 5/17 7/27 9/30
1963 3/29 3/30 5/19 8/6 9/4 181

1964 4/14 4/21 5/19 7/23 229

 

I.
-, '-i e inn-4- ware -' -.
' tf‘fxiffl nfi

t

 

65

Vegetative Apex: The vegetative apex presented a rather flattened
buttress with leaf primordia cut off in an alternate arrangement (Figure
lO-B). The buttress showed a slightly curved surface made up of a 2

layered tunica and a corpus 2 or 3 cells deep.

Floral Apex: The first indication of flower formation became
evident in early September at which time several raised areas of
meristematic cells were visible (Figure lO-C). These highly meristematic
cells continued to differentiate rapidly until approximately mid—September
when individual floret primordial masses could be distinguished (Figure
lO-D). These primordial masses were rounded in shape with a slight
flattening of the apex. A definite flattening of the buttress was not evi-
dent, however, until approximately 5 days later (Figure lO—E). The
primordial mass was still highly meristematic with activity in the lower
part of each floret decreasing. Cell division and expansion did not stop
entirely until the floret peduncles had been differentiated.

A few days after the buttress flattened out the sepals first became
evident at a time when the buttress was a slight concave, dish—shape
(Figure lO—F). Although the stamen primordia followed the petal
primordia within 3 days in early October, the undifferentiated buttress
surface continued to be slightly concave (Figure lO=G). Protuberances
indicating carpel primordia became evident within 2 or 3 days after the
stamen primordia (Figure lO=l—l), at which time meristematic activity
continued rapidly with carpels and minute ovules formed by late October
(Figure 10=l). Also, microsporogenesis was noticed to be proceeding
rather rapidly. Each floret was complete in all flower parts at this time
except for completion of microsporogenesis and megasporogenesis.
Normally microsporogenesis was not completed and megasporogenesis
apparently did not begin until growth resumed in the spring (Figure

lOmJ).

 

1- (.

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-u- .

..-._-.,_,;. , baaodl “nu"

:1 I: 'J-
__._-:,.-_.-3 film‘s-1.38"”: ~

 

 

Figure 10: Stages in the development of Spiraea thunbergi Sieb.
flower buds.

A
B
C
D
E.
F
G
H
I
J

. Vegetative (middle) and flower buds' (upper bud).
Vegetative apex (approx. 40x).

. Floret initiation, first appearance (approx. 40x).
. Individual florets visible (approx. 40x).

Floret buttress flattened (approx. 40x).

. Sepal primordia (approx. 80x).

Petal and stamen primordia (approx. 40x).

Carpel primordia (approx. 40x).

. Ovule development (approx. 40x).

. Flower before anthesis (approx. 40x).

67

 

 

68

A few flOWers were observed to bloom in late October, depending
upon weather conditions, with microsporogenesis being completed but
it was not determined whether megasporogenesis had been completed.

Anthesis started in the early spring after 5 or 6 days of warming
weather. The period of bloom extended over a l to 2 month period.

Flower initiation began in early September after approximately
125 days of vegetative growth. Three to five rounded primordial masses
were at first evident, eventually becoming flattened. Sepals, petals,
stamens and carpels were initiated in acropetal succession from late
September to mid-October. Microsporogenesis began several days
later. Megasporogenesis was not observed in the fall but appeared to
be completed a day or 2 before anthesis the following spring. Anthesis
normally occurred early in the spring, although it did also occur during

the fall months ..

Viburnum dentatum L. (Caprifoliaceae Vent.,
Section Odontotinus Rehd.)

Gross Morphology: The period of vegetative growth started from
mid to late April and continued uninterrupted until mid=July. Buds
during this time were small and flower and vegetative buds were not
distinguishable. Toward the end of July, growth began to decrease and
the terminal buds began to enlarge. Large plump buds were evident
from early August until shortly before vegetative growth commenced
the following spring (Figure ll=-A).

During the fall and early spring inflorescences were developing
in the terminal buds. Shortly after vegetative growth commenced in the
spring, the mostly undifferentiated floral primordia continued to develop
at the same time as stem growth. By the time of anthesis, the vege—

tative stem growth had elongated about 5 inches. At the same time, the

     

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69

Cymose inflorescence continued development until anthesis in early to
mid-June.
Most fruit had matured and abscissed by the time floral initiation

becomes evident.

Table 14: Growth Characteristics of Viburnum dentatum L.

 

Days from

 

Vegetative Flower Buds Date of Inflorescence
Growth Flowering First Visible Initi- Initiation to
Year Began Began Ended to Naked Eye ation Flowering
1962 4/24 6/8 6/23 9/15 Inflorescence
9/3, Flower
4/14
1963 4/17 6/12 6/28 9/4 Inflorescence 282
9/10, Flower
4/16
1964 4/18 6/8 6/23 271

 

Vegetative Apex: The typical vegetative apex showed a shallow
convex buttress. The tunica of the apex consisted of 2 layers with a
rather disorganized corpus approximately 4 cells thick and located
immediately below the tunica. Leaf primordia are oppositely arranged

and arose on the flanks of the buttress (Figure 11=B).

Floral Apex: Inflorescence initiation became evident during early
September approximately 38 days after the previous bloom. At first the
buttress was ahllow with somewhat more width than the vegetative apex
(Figure ll=-C) but soon began to rise rapidly in the center. The primordial
mass grew rather rapidly until individual floret primordia were evident
in a highly undifferentiated state (Figure ll—D and E). At this time the

visual appearance of the flower bud produced a compressed, plump

    

3.x.

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-_ ' .- '-:'...- " «i. ..! lir'é'.t'.--- -,,._.-, f.- aunts-bull

   

 
   
  

      
 

 

'- .mubno

70

appearance and all flower primordia remained in this condition until
resumption of growth the following spring.

Upon resumption of growth (mid-April), the ”ball" shaped in-
florescence began to expand and soon emerged from the bud scales.

At the same time the pedicels of the cymose inflorescence expanded
causing the ”ball" shaped primordial mass to expand in width; individual
flower initiation could be observed (Figure ll-F). The typical buttress
surface became shallow and concave in shape and the individual cymes
of the compound inflorescence were conspicuous. The sepals became
evident at the same time or within a few days.

The sepals, petals and stamens followed in rapid succession
(Figure ll-F, G. and H) so that by early to mid-May these floral parts
were well-developed. Initiation of the petals and stamens was observed
to be either simultaneous or the stamens followed in quick succession.
While the sepals, petals and stamens were forming, the inflorescence
branching system was also expanding to its maximum width (Figure ll-G).

Carpel development could be observed during early May with ovule
formation evident during mid-May (Figure ll-l).

Microsporogenesis and megasporogenesis were limited to the last
2 weeks of development immediately preceding anthesis (Figure ll—J).

Inflorescence initiation and development occurred after vegetative
growth had ceased during early to midmautumn. The flower primordial
mass over-winters in an undifferentiated state. Soon after vegetative
growth commenced in the spring individual floret initiation began (mid-
spring). Sepals, petals, stamens and carpels were initiated rapidly in
acropetal succession. Microsporogenesis and megasporogenesis were

limited to the last 2 weeks of flower development.

 

- - ' i " _ -e_."'_-.'-.-:.m§3
.q‘nntji Wilt!“ . . '
.J-_ l_.
.. , 4,») , :a.‘01!ai0 MW '1
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. . -.« l a-rus‘ W” _ .91.“?

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.-rr_-."1

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Figure ll:

71

Stages of flower development in Viburnum dentatum L.
and \_’. lentago L.

A.

O’TJP'JUOW

'.'E

Exterior of flower buds; V. dentatum left and
V. lentago right.

. Vegetative apex (approx. 35x).

. First indication of floral initiation (approx. 35x).
. inflorescence primordia (approx. 30x).

. Floret primordia (approx. 30x).

. Sepal initiation (approx. 45x).

. Petal and stamen primordia simultaneous or stamens

somewhat later (approx. 40x).

. Carpel initiation (approx. 40x).
. Ovule formation (approx. 35x).

. A day or two before anthesis (approx. 15x).

72

«92%»

   

 

 

73

Viburnum lentago L. (Cairifoliaceae Vent. ,
Section Lentago DC)

 

Gross Morphology: The period of vegetative growth began in
mid-April and continued until the end of July. During the early stages
of development flower and vegetative buds were not distinguishable.

By the end of June the basal area of the terminal bud began to swell
indicating floral development had begun. This swollen area continued
to enlarge until it was approximately one-quarter inch in diameter by
the onset of dormancy. The bud remained in this condition until vege-
tative growth started in the spring (Figure ll-A)

Inflorescence development commenced during mid to late summer
with floret development beginning during early autumn. With the com—
mencement of vegetative growth the following spring, the inflorescence
and flowers continued development until anthesis in mid to late May.
Flowers were borne on previous season's wood. Current season vege-
tative growth surmounted the inflorescence by mid-June.

Fruit development and the development of the inflorescence pro-
ceeded at the same time with the fruit reaching maturity at approxi—

mately the same time individual flowers were initiated.

Table 15: Growth Characteristics of Viburnum lentago L.

 

 

Days from

 

Vegetative Flower Bud Date of Inflorescence
Growth Flowering First Visible Initi— Initiation to
Year Began Began Ended to Naked Eye ation Flowering
1962 4/9 5/19 5/27 7/10 Inflorescence
6/23, Flower
7/16
1963 4/2 5/19 6/5 7/20 Inflorescence 330
6/19, Flower
7/24

1964 4/16 5/17 5/28 7/2 333

 

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74 \

Vegetative Apex: Similar to the vegetative apex of Viburnum
dentatum L. (Figure ll-B).

Floral Apex: Inflorescence initiation was observed from mid to
late June approximately 20 days after the previous bloom (Figure ll—C) .
Development of the inflorescence primordial mass was like that of
Viburnum dentatum L. (Figure ll-D) . Floral primordia became evi-
dent by late July when the inflorescence mass appeared to flatten in
shape and segregate into individual flowers (Figure ll—E) . Cymes were
Well-developed by early August with sepals apparent (Figure ll-F) .
Petal initiation followed 18 days later and the primordia of the petals
and stamens appeared to arise either simultaneously or in quick
succession (Figure ll-G and H). The carpels did not appear to be
completely formed at the time dormancy set in. At this time the ‘visual
appearance of the flower bud produced a candle-like appearance with a
swollen base. The inflorescence and individual flowers remained in
this condition until growth resumed the following spring.

With the resumption of growth the next spring, the cymose
inflorescences expanded rapidly until they had become flattened in shape
16 days preceding anthesis. During the time of inflorescence expansion
the individual flowers completed development.

Ovule development was observed to be well underway 14 days
after resumption of growth and 30 days preceding anthesis (Figure ll—I).
The beginning of megasporogenesis and microsporogenesis, however,
was not observed until approximately 16 days preceding anthesis
(Figure ll=J).

Initiation of the inflorescence occurred in mid=surnmer as vege-
tative growth began to slow up. Flower initiation began 35 days after
the inflorescence was initiated. Sepals, petals and stamens were laid
down in early fall and were fairly well developed when cold weather

began. Carpels apparently made little development in the fall but

 

75

developed rapidly after growth resumed the following spring. Floral
parts were initiated in acropetal succession. Microsporogenesis and

megasporogenesis were limited to the 16 days preceding anthesis.

       

.'I ;:!.- I'll
-.-. -..n.snassol1bi' :' " .

  

--.H n'. “mm-rerun?”-

 

 

75 b
I

developed rapidly after growth resumed the following spring. Floral

parts were initiated in acropetal succession. Microsporogenesis and

megasporogenesis were limited to the 16 days preceding anthesis.

 
    

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CONCLUSION

In Table 16 a comparison of vegetative growth, flower bud
formation and flowering periods is made for all the species examined.

Vegetative growth in all plants was found to start during late
April or early May regardless of the time of flowering. In agreement
with Goff (1899, 1900, 1901) vegetative growth was observed to have
ceased when flower buds became visible to the naked eye except in
Hibiscus syriacus L. and Indigofera potanini Craib.

Flower bud formation and flowering, on the other hand, Were
found to vary with the time flowering first occurred.

All the spring flowering plants--Hamamelis vernalis Sarg.,
Cornus rgas L., Forsythia olaia Nakai., Prunus glandulosa Thunb. ,
Spiraea thunbergi Sieb. and Viburnum lentago L. --except Prunus
glandulosa Thunb. and Spiraea thunbergi Sieb., were found to initiate
flowers during the early part of the previous summer. Both Prunus
glandulosa Thunb. and Spiraea thunbergi Sieb. initiated flowers during
the latter part of summer similar to several other genera of rosaceous

plants (Goff, 1899, 1900, 1901; Drinkard, 1909; MacDaniels, 1922;

Tufts and Morrow, 1925; and Hirai, Nakagawa, Nanjo and Hirata, 1961).

Summer flowering plants—nPyracantha coccinea Roem. var.

lalandii Dipp., Rosa multiflora Thunb. , Viburnum dentatum L.,

 

Hibiscus syriacus L. and ~Lngfigofera potanini Craib. c-Were found to

vary considerable in the time of flower initiation. Hibiscus syriacus L.
and lies—a multiflora Thunb. initiated flower buds in late April or early
May, resembling the spring flowering plants. Time of flower initiation

for Rosa multiflora, Thunb. was similar to that found by Grainger (1939)

76

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for 3% <_:a_ni£1_a L., in England. Both plants initiated flowers in late
April and flowered from mid to late June. Viburnum dentatum Lo and
Pyracantha coccinea Roem‘, var“ lalandii Dipp. which flowered during
early summer were found to initiate inflorescence primordia in late
summer and late autumn, respectively, but did not initiate floret
primordia. Inflorescence and flower initiation and development of
Pyracantha coccinea Roemo lalandii Dipp. was found to correspond with
results found by Reisch, Chadwick and Hildreth (1961) and Girouard
(1962).

Flower initiation and development in lndiogfera potanini Craib.
were most interesting, Although this plant flow/cred all summer the
majority of flOWers were borne during the first 3 or 4 weeks of the
season, the amount of flowering decreased from that point until flower-
ing stopped in late September. In addition, flower primordia were
formed throughout the flOWering period and into the autumn. Within the
multiple winter buds as well as within individual racemes 2 or 3 stages
of development of miniature flOWer primordia Were found; Microscopic
examination of these buds revealed that the order of flower part
succession was similar to that found by Goebel (1887).

The length of time over which vegetative growth progressed was
a factor in the initiation of flower buds in plants which flowered in the

autumna The amount of vegetative growth of Hamamelis virginiana L.

 

and Hamamelis vernalis Sarge Were similar“ Vegetative growth of

E“ vernalis Sarg., was more vigorous and flower buds appeared to
develop more abundantly under cultivation than those of :1 virginiana Lo
Although I: virginiana L., flowered in mid to late autumn and I1 vernalis
Sargu flowered in very early spring, the time of flower bud initiation of
each species was within 5 or 10 days of one another. Fruits of 11
vernalis Sargv matured the same year as anthesis and fruits of

I_-1‘, virginiana Lu mature 1 year after the flowers opened“

        
 
   

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Results obtained in this study generally agree with the order of
succession in papilionaceous legumes (Goebel, 1887), rosaceous fruit
crops (Goff, 1899, 1900, 1901), loquat (Smock, 1937), cranberry
(Lacrois, 1936), lowbush blueberry (Bell and Burchill, 1955),
Gaultheria species (Chou, 1952) and Populus species (Nagarij, 1952).

The results of the present investigation were intended to serve
as a guide for experiments on cultural methods similar to those for
tree fuits (Ruth, 1921; Harley, Masure and Magness, 1932; Crane and
Dodge, 1935; and Edgerton and Harris, 1950)., In addition these data
were prepared as a beginning for further work on the ecology of flower-
ing of woody ornamentals to aid the understanding of their responses

to various environments .,

 
 

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LITERATURE CITED

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BAILEY, L. H. 1949. Manual of cultivated plants. The Macmillan
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BAJPAI, P. N. and R. K. SHUKLE. 1962. Blossom bud differentiation
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BALL, E. 1927. The time of differentiation and the subsequent
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BELL, H. P. and J. BURCHILL. 1955. Flower development in the
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BOODLEY, J. W. and J. W. MASTALERZ. 1959. The use of
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BRADFORD, F. C. 1915. The pollination of the pomaceous fruits.
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CANNON, T. F. and J. B. GARTNER. 1963. The effect of malic
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CHADWICK, L. C., K. W. REISCH and P. TRAYLOR. 1959. The
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CHOU, Y. L. 1952. Floral morphology of three species of Gaultheria.
Bot. Gaz. 114: 198=2.Zl,

80

  
   

 

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81

COULTER, J. M. and C. J. CHAMBERLAIN. 1903. Morphology of
angiosperms. D. Appleton and Co., pp. 16==20.

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DAVIS, L. D. 1957. Flowering and alternate bearing. Amer. Soc.
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DOWNS, R. J. and A. A. PIRINGER, JR. 1958. Growth and flowering
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DRINKARD, A. W. 1909=1910. Fruit bud formation and development.
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EDGERTON, L. J. and R. W. HARRIS. 1950. Effect of nitrogen and
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EGGERT, F. P. 1957. Shoot emergence and flowering habit in the
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FATTA DEL BOSCO, G. 1961. Indagini sul'epoca di differenziazione
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FOERSTE, A. F. 1891. On the formation of the flower buds of spring=
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FURR, J. R. and W. W. ARMSTRONG. 1956. Flower induction in the
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GARDNER, V. R., F. C. BRADFORD and H. D. HOOKER. 1952.
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GARTNER, J. B. and M. L. McINTYRE. 1957. Effect of day length
and temperature on time of flowering of Euphorbia pulcherrima
(Poinsettia). Amer. Soc. Hort. Sci., Proc. 69: 492=497.

 

     

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82

GIROUARD, R. M. 1962. The ontogeny of the perianth, stamens
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1900. Investigations of flower buds. 17th Ann. Rept.
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1901. Investigation of flower buds. 18th Ann. Rept. Wisc.
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HARLEY, C. P., M. P. MASURE and J. R. MAGNESS. 1932. Effects
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HUBBELL, D. S. 1934. A morphological study of blind and flowering
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83

ISBELL, C. L. 1928. Growth studies of the pecan. Ala. Poly. Inst.
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l

KOSUGI, K. Dept. of Horticulture, Chiba University, Matsudo, Chiba-
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MACDANIELS, L. H. 1922. Fruit bud formation in Rubus and Ribes.
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MACLEAN, D. C. 1962. Floral initiation and expression in Wei ela as
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Hort. Sci., Proc. 40: 111E112.

 
    
 

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84

RANDHAWA, G. S. and H. S. DINSA. 1947. Time of blossom-bud
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Ontogeny of the inflorescence of Pyracantha coccinea lalandi.
Abs. 58th Ann. Meeting Amer. Soc. Hort. Sci., Purdue Univ.

 

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85

SINGH, J. P. and H. S. DHURIA. 1960. Studies on blossom-bud
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