' ' 1.x? 4k.” .‘.‘.\‘\JL5 ‘u‘s u‘r“.. '.~'..‘- \I. .-..

.0‘ UL...

' ' ‘1‘ ‘- "t" ' '22!" ”r: -‘*~.u ;\ .* w 'st'\’.":‘*2’“=! 51‘2”

r, ‘ “ a ' - r. 7:.
‘ 9 ' ‘ ‘ "" ‘ .5; a:
. . bx»,-

b
0"

x a . .- 9 -.-.;. 4" a (”-f‘x -. - ~‘ 9
M “ x 3 u 2. 4 1
..-- x.“ :‘Juxn a. r."t..'.- ux. ...;4x .-.A
. w
t.“ ) l’\‘x .' _ .‘ . --a
- ' "‘ ' "Q- ”-5 R 1' "a 39 "‘ :‘k w? A
v .‘ ‘. ‘ E ‘- . . ,‘ d .- " .
.v’ 'o ‘. It; . k, d s a. u 1 a \l k' S '3. E1, .

’ ”EEC!“ _ ’ ' .»

Ill/Il/l/ll/l[IN/1111177111117117111111i _ ~ ‘

39917

. mush *‘n - , w .- .4 _ .214.- 1 -4c-__‘,__.

This is to certlfg that the

thesis entitled

The INFLUENCE OF DAYLENGI'H A*D
TEMPERATURE UPON THE FLOWERII‘J‘G
OF VIOLA ODORATA

presented by

\ 1 Calvin C. Cooper

has been accepted towards fulfillment
of the requirements for

_M‘_S'___ degree in_.H_ orti 0 U1 tUI‘e

W‘ P LL} (311843-11

Major professor

Date July 17, 1951

 

0-169

 

w fr¥””’m .V:4J

“‘\
1-K
.

 

MSU

LIBRARIES
fl

 

 

 

RETURNING MATERIALS:
PIace in book drop to
remove this checkout from
your record. FINES wiII
be charged if book is
returned after the date
stamped be10w.

-_.—-——

 

 

 

W!

 

 

T7254“

 

 

 

 

 

 

’3‘
{Wu
DJV
"a
VI‘A
..

 

 

THE INFLUENCE OF DAYLENGTH.AND TEMPERATURE
UPON THE FLOWERING OF VIOLA ODORATA

BY

.Calvin Charles Cooper
N

A THESIS
Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Horticulture

1951

ACKNOWLEDGEMENT

The author wishes to express his gratitude to
Donald P. Watson for critical suggestions and aid
which have been of considerable value in the prepara-
tion of this thesis. Appreciation is also expressed
to waiter J. Haney and Paul R. Krone for helpful

suggestions, and to Paul Andrews for taking the photo-
graphs 0

n. ‘2. ; ~..~ j. a 4-

TABLE OF CONTENTS

mRODUC T I ON C O O O O 0

LITERATURE REVIEW. . e .
History. I e 0

Influence of Light Intensity

Influence of Photoperiod . .

Influence of Temperature

Morphology e e e e e e 0

Descriptive Morphology

PROCEDURE. 0 e o e e e 0
DISCUSSION OF RESULTS. .
Vegetative Growth .

Leaf Size. . .‘

Leaf Number. 0

Stolonifercus Growth
General Influence of

O

O

O

O

O

O

r

0

Temperature

and

Photoperiod o e e e e e e e e 0

Influence of Phetoperiodic Change.

Reproductive Growth . . . . . . . . .

Chasmegamous Flower Production .

Cleistogamous Flower Production.

Reversal of PhotOperiod. . . . . . .

Influence of Leaf Type on Flower Type.

Application to Greenhouse Operation. . . .
SUMMARY. 0 O O O O 0 O O I O O O O O O 0 O 0 O I
BIBLIOGRAPH O O O 0 O O O O O O O O O O O O 0 O O O

0.

page

{D O) (h 01 IF CR 0| (fl

5555?:

16
16
18
18
19
20
21
23
25
28

INTRODUCTION

The production of violets (Ziglg odorata) as a come
mercial greenhouse crop has become less common in the
central and eastern United States during the last thirty
years because of the difficulties encountered in timing
the crop to coincide with the demand. When Easter and
Mother's Day_have occurred late in the spring, flowers
have been of a poor quality and production has almost
ceased. 1

The violet produces the attractive chasmogamous
flowers when the plants are exposed to a short daylongth
for an extended period of time. Inconspicuous cleisto-
gamous flowers are formed when the plants are exposed
to a long photoperiod. Consequently, shortening the
photoperiod could logically extend the period of come
,mercial flower production into the more desirable spring
months.

Egglglodorata is not unique in its growth.response
to changes of photoperiod. A large number of the plants
that respond to photoperiod give very unlike responses
at different temperatures. For example, Roberts and
Struckmeyer (1939) studied the influence of temperature
on the response of a large number of plants to photo-

period. They found that Antirrhinum.majg§'and Petunia
hybrids would flower only under long days at a temperature
above 65° F. If the temperature were lovered to 55° F.,
however, these species would flower under any daylongth.
High.temperatures have been used to produce the same
effect as long days for the purpose of inducing formation
of flowers on Rudbeckia bicolor (Murneek, 1940).
Suggestions by Post (1949) as well as results by
Murneek (1940), Roberts and Struokmeyer (1939), Madge
(1929) and others, stimulated a desire to investigate
the influence of temperature on the response of 22212.
odorata to photoperiod. In addition, it was desired to
study the length of time required for chasmogamous and
cleistogamous flowers to appear after the beginning of a
favorable photoperiod. This might be of considerable

value to commercial greenhouse operators.

REVIEW OF LITERATURE

History. It has been known for many years that
plants of the genus Eiglg produce chasmogamous and cleisto-
gamous flowers. muller first made this observation in
1857 and at that time described the cleistogamous flowers
of six species (Madge, 1929).

Ipfluence of Light Intensity. Most of the work which
has been done with the influence of light intensity on
the growth.of Eiglg_has been with.reference to its affect
on flowering. It has been stated however that the plants
_of Eigl§_grow best under a maximum.light intensity of
1200 foot candles (Post,1949).

An attempt to prolong the production of chasmogamous
flowers of yiglg'odorata was reported by Bradley (1901).
Eb could prolong flowering two or three weeks by reducing
the light intensity during the last week in February.
Madge (1929), however, found no difference in the period
during which.chasmogamous flowers were produced in the
shaded and the sunny outdoor plots. She did obtain
relatively more chasmogamous flowers from the shaded plots
and also more cleistogamous flowers on the plants that
were grown in full sunlight.

Ipfluence of Photoperiod. The flowering habit of
Xigl§.has been described as being indeterminate, by Allard
and Garner (1940), with.the completeness of the flower
produced depending upon the length of the photoperiod.

The first extensive research concerning the affect
of length of day upon the flowering of many species of
plants by Garner and Allard (1920) included 21212.£$Ef
briatula. They found that when plants of Xiglg_fimbri-
gtglg'var. J. E. Smith.were exposed to 7 hours of light
followed by 17 hours of darkness, they produced purple
chasmogamous flowers in one month. A few cleistogamous
flowers were also produced by this treatment. Plants
eXposed to a normal daylength in June and July at Belts-
ville, Maryland, produced numerous cleistogamous flowers,
but no chasmogamous flowers.

In later work‘both.!igla fimbriatula var. J. E. Smith
and Eiglg_papilionacea var. Pursh.were observed to produce
chasmogamous flowers under a daylength of 10 to 12 hours.
In addition; long days tended to increase the plant vigor
and to cause the formation of excessively large leaf blades,
long petioles, and cleistogamy; while short days tended to
cause the development of small, short petioled leaves and
chasmogamous flowers (Allard and Garner, 1940).

Similar results have been obtained by other investi-
gators. Madge (1929) found, that at Royal Halloway

College in England, Viola odorata produced chasmogamous

,‘

,Q

flowers between September and March and cleistogamous
flowers between May and September. In 1932 Bergdolt
observed that cleistogamous flowers were produced under
conditions favoring large amounts of vegetative growth

and also that the production of chasmogamous flowers was
favored by a reduction in foliage either by surgical or
nutritional means. It was believed that the most important
factors having a definite influence on the morphology and
physiology of Xigl§_odorata were a combination of light,
moisture, and nutrition (Bergdolt, 1932).

Influence of Temperature. w m and E213
gylvestris produced cleistogamous flowers under a photo-
period Of 16 hours, if the temperature permitted what was
termed by Chaurod (1947) as "active growth”. He Obtained
no chasmogamous flowering in these two species under a
photoperiod of eight hours duration and a temperature of
55° to 59° F. from October to May. A few pale colored
flowers were produced during April under the eight hour
photoperiod and natural outdoor temperatures. He concluded
that chasmogamous flowers were produced by these two
' varieties under short days only if there was a 'rhythm.of
warmth and cold in the temperature". This did not appear
to refer to diurnal temperature fluctuations, but to

changes over a longer period of time.

Morphology. Madge (1929) catalogued the flowers
produced by Ziglg_odorata var. praecox into three types:
cleistogamous, semi-cleistogamous, and chasmogamous. She
found that the semi-cleistogamous flowers, an intermediate
type showing several stages of transition between the two
extremes, was produced during a short period in the spring
and fall. The semi-cleistogamous flowers resembled the
cleistogamous flowers in the complete absence of a spur
and nectary and would be classified as a cleistogamous
flower by a taxonomist recognizing only two types of
flowers.

Chasmogamous and cleistogamous flowers undergo the
same stages early in their development. The ovules,
however, differentiate earlier in the cleistogamous
flower. The cleistogamous flowers appear incomplete in
their development, but the flower structures in these
flowers resemble those in the chasmogamous blooms in
number and arrangement of parts. Many of the structures
in the cleistogamous flowers remain in an undeveloped
stage and only those parts essential for the protection
of the reproductive organs and for seed production are

fully developed (Theron, 1939).

Descriptive Morphology, In order to clarify the
following description of the flower types, four diagrams
of the flowers of Viola odorata are presented in Figure 1.

In the cleistogamous flower, A, there are five normal

 

 

.. -
.
I
.. ....
~ ‘
e
.
' O
m
...
O
. _ .
.
.
. .
, u
.
- .
. .- .
O -- I
.
. .. .. ....... ,r
‘
... . .. ....

 

Fig. 1. Diagramatic drawings of the flcwer types
of Viola odorata. A. a mature cleistogamous
flower; B. a longitudinal section of a cleistog-
amous flower; C. a mature chasmogamous flower;
D. a longitudinal section of a chasmogamous
flower.

 

sepals which.enclose the flower and show no signs of opening
until the fruit is formed. The cleistogamous flower, A, is
illustrated with the fruit fully formed and the tips of the
sepals spread apart making the ovary visible. The petals,
when present, are 2 to 5 in number and take the form of
small membranous strap shaped, almost entirely unpigmented
structures. The corolla may be entirely missing as in B.
The androecium.consists of five stamens which.eerve in
self pollination of the flower as shown in B, Figure l.
The gynaecium is made up of a normal ovary, containing
three carpels with three parietal placentae, and a
modified style and stigma. The style is bent over to
form.a hook, thus'bringing the stigmatic surface closer
to the pollen sac of the two anterior stamens. The bent
style it shown in B, Figure l, but the stigmatic surface
does not appear to be near the pollen sacs of the stamens
because of the maturity of the flower illustrated (De-
scriptions after Gorczynski, 1952; Rests, 1931; Theron,
1939).

In the chasmogamous flower will be found five free
petals, C, Figure 1, alternating with.five free sepals
(not shown). The anterior petal contains a long hollow
spur acting as a protective sheath for the nectary spurs
and as a storage reservoir for the nectar. In the repro-
ductive part of the flower are five free stamens. Two
stamens are inside the anterior petal and have the nectary

spurs attached. One of the stamens shown in D, right, is

a
..
.
t
C
O .
e
.
1
.
. ‘ - -
'
M
.
__
U
.
w
‘ -

,‘

,C

I.

 

 

inside the anterior petal and the nectary spur is attached
to it. The ovary is made up of three carpels and has
three parietal placentae. Two of the placentae are shown
in D, Figure 1, with abortive seeds attached (Description
after Madge, 1929).

One fertilized ovule is found in the ovary of the
cleistogamoum flower B, in contrast to an absence of
fertilization in the ovary of the chasmogamous flower D,
Figure 1. This is typical of Eiglg_odorata in which only
the cleistogamous flowers produce seed. In a few species
such.as Eiglgbriviniana, as a result of variations in the
structure of the androecium and gynoecium, both flower

types prouuoe seed (Description after waste, 1931).

PROCEDURE

On October 15, 1950, one hundred seventy-five young
plants of Eiglg.od0rata var. Fries Favorite were planted
in a sterilized soil (50 per cent peat and so per cent
sandy loam) in four inch pots. The plants were placed in
the plant science greenhouse at Michigan State College
under a 50 degrees Fahrenheit night temperature (50° F.N.T.).
After 3 weeks, four groups of 43 plants per group were
selected for uniformity among the groups. Two groups were
grown in one greenhouse with a 40° F.N.T. and the other
two were grown in another greenhouse at 50° F.N.T. In
each of these two houses one group was supplied with.a
16,and the other group with.an 8 hour period of light.
The resultant treatments were:

I. 40° F.N.T., 15 hr. photoperiod
II. 40° F.N.T., 8 hr. photOperiod
III. 50° F.N.T., 16 hr. phot0period
IV. "50° F.N.T., 8 hr. photoperiod

The temperature was controlled in all treatments by
automatic thermostats. In groups I and II, automatically
controlled ventilators enabled accurate control of temp
persture. In treatments III and IV it was necessary to

use slightly less accurate manually operated ventilators.

10

The long light period in treatments I and III was
kept constantly at 16 hours. Natural day 1ength.was
extended by the use of incandescent lights giving a light
intensity of approximately 15 to 25 foot candles at the
leaf surface. The 8 hour photoperiod was obtained in
treatment II by the use of a covering of black sateen
cloth.and in treatment IV by moving the plants into a
connecting dark room.kept at the same temperature as
the greenhouse.

Soil tests were made every two weeks. A balanced
complete soluble fertilizer was applied in solution as
needed to attempt to maintain the nutrients at the
following levels: nitrogen, 20 to 50 ppm. spurway; phos-
phorus, 5 ppm. spurway; potassium, 10 ppm. spurway. The
pH of the soil was from 5.5 to 6.5.

On December 7, 1950, four weeks after the treatments
were begun, all of the flower buds visible on the plants
were removed, assuming that these buds had been initiated
before the controlled conditions were supplied. On
January 6, 1951 (four weeks later) and at regular weekly
intervals thereafter, all of the flowers were cut and a
record was made of the number of the chasmogamous flowers
produced. A record was also made of the peduncle length
and the diameter of the flowers in inches from.the tips
of the Opposite petals adjacent to the anterior petal.

On February 9, 1951, 15 weeks after the treatments

‘were begun, ten plants were selected at random from.each

TABLE I

MEAN WEEKLY TEMPERATURES FOR 40° AND 50°
FARRENHEIT NIGHT TEMPERATURE (F.N.T.) HOUSES

W

 

 

week 40° F.N.T. ' 50O F.N.T.
- night day night day
14 41 47 52 59
15 42 50 52 60
16 42 55 54 62
17 41 49 52 61
18 44 55 55 66
19 45 61 56 67
20 49 56 54 61
21 45 65 54 67
22 42 50 50 58
25 44 58 51 64
24 54 76 59 77

25 53 72 .59 _ 76

 

11

treatment. These groups of ten plants each.were moved to
the Opposite photoperiod at the same temperature at which
they had been growing and records were continued as pre-
viously with.the addition of the four new groups. There-
fore, after February 9th there were the following eight
groups of plants under observation:
I . 40° F.N.T., 16 hr. photoperiod 55 plants
IA. 40° F.N.T., 16 hr. photoperiod 10 plants
previously 8 hr. photOperiod
II . 40° F.N.T., 8 hr. photoperiod 55 plants
IIA. 40° F.N.T., 8 hr. photoperiod 10 plants
previously 16 hr. photoperiod
III . 50° F.N.T., 16 hr. photOperiod 55 plants
IIIA. 50° F.N.T., 16 hr. photoperiod 10 plants
previously 8 hr. photoperiod
Iv . 50° E.N.T., 8 hr. photoperiod 55 plants
IVA. 50° F.N.T., 8 hr. photoperiod 10 plants
previously 16 hr. photoperiod
All plants were transferred to 6 inch pots on March
17, where they remained until the end of the experiment.
On May 8, 1951, 25 weeks after the original treatments
were begun the experiment was discontinued because it
was difficult to maintain 40 and 50° F.N.T. (Table I).
Leaf area of ten plants from each.group was measured.
with.a planimeter to compare the vegetative growth in
each treatment.

To get an indication of how long the plants could be

kept flowering in the spring of the year, twenty plants
were retained after May 8th.under an eight hour daylength.

The temperature during this period rose considerably above
the 50° F.N.T.

 

Fig. 2. Violet plants after eXposure to 17 wgeks

of long or short days in the greenhouse at 50 F.
night temperature.

  
  

 

    

:9
I
if

e y

i '1 # ‘1')".

     
 
 

,. ”'5'
K

 

ugx:
~ . ‘I\ J... a ‘
O

"-l..
7'.
A._'-.
.r‘ z,
i .
.“.'
A o‘
U

  
     
 

'- ’-

   

( . .

'v

n
'5-
,
.
C

 
 

    
  

     
   

\
v

. J

O

‘3."
a! ,

.

 
  

‘\
\nh
‘.

LB. '1

Fig. 3. Violet leaves and flowers showing the

e
. e

 
 
 

a

4

 

I
k‘ .-
0
I
I
.
J.
.n O
I
' 4
‘ o
e l. )
' l

9

relative size after 25 weeks of long or short days

in the greenhouse at 500 F. night temperature:
Left, chasmOgamous flowers and small leaves pro-
duced during short days; Right, cleistogamous

flowers and large leaves produced during long days.

TABLE II

INFLUENCE OF TEMPERATURE AND PHOTOPERIOD
ON VEGETATIVE GROWTH

 

E-

 

 

 

 

Average Average
Treatment number of leaf area Average area
leaves per per plant in per leaf in
plant square inches square inches
Long days for
25 weeks
III 50° 61.8 421.8 7.0
I 40° 59.4 525.0 8.4
Short days for
25 weeks
IV 50° 47.0 161.0 5.5
II 40° 41.8 184.7 _ 4.5
L.S.D. .05 9.1 52.5 .8
L.S.D. .01 12.5 45.5 1.1
Short days for
15 weeks
followed by
long days for
12 weeks
IIIA 50° 52.2 525.1 6.4
IA 40° 50.9 245.4 8.1
Long days for
15 weeks
followed by
short days for
12 weeks
IVA 50° 51.7 228.4 4.5
IIA 40°_. 44.4 225.5 5.1

 

DISCUSSION OF RESULTS
Vegetative Growth

Leaf 81263 Figure 2-is a photograph.of a group of
plants from.the long and short photoperiodic treatments
in the 50° F.N.T. 17 weeks after the treatments were
initiated. The most obvious response of this species to
a 16 hour phot0period is the development of large leaf
blades on long petioles, making a muoh.more vigorous
plant in contrast to the smaller leaves and shorter
petioles produced on less vigorous plants grown under the
short photoperiod of 8 hours. To further emphasize this
difference separate leaves have been removed from plants
in each treatment (Figure 5) after 25 weeks. The re-
sultant plant growth.was comparable to that found by
Allard and Garner (1940). '

A comparison of leaf areas after 25 weeks as in-
fluenced by both.temperature and length of photoperiod
is shown in Table II. The average total leaf area per
plant in the long photoperiodic treatment at 50° F.N.T.
was found to be 98.8 square inches greater than the.
average total leaf area per plant in the long photoperiod
at 40° F.N.T. This was significant at the l per cent
level. No significant difference at the 5 per cent level

 

Fig. 4. Violet plants showing the relative size
after 25 weeks of long or short days in a green-
house at 40° F. night temperature.

 

Fig. 5. Violet plants showing the relative size
after 25 weeks of long or short days in a green-
house at 50° F. night temperature.

14

was found between the average total leaf area per plant
in the short photoperiod treatments in the 40 and 50°
F.N.T. As would be expected from the data presented in
Table II and Figures 4 and 5, highly significant differ-
ences (at the l per cent level) were found in the total
leaf area per plant between the long and short photo-
periOd treatments for 25 weeks at the given temperatures.
At the 50° F.N.T. there was a difference of 260.8 square
inches, and a difference of 158.5 square inches at 40°
F.N.T.

The leaves on the plants in the 40° F.N.T. and long
days were found to be on the average 1.4 square inches
larger than the leaves on the plants in the 50° F.N.T. long
day treatment. Likewise the leaves on the plants in the
short days at 40° F.N.T. were found to be on the average
1 square inch larger than the leaves on the plants in the
50° F.N.T. short day treatment. The differences between
temperatures were significant at the 5 per cent level for
the short day treatments and at the 1 per cent level for
the long day treatments. This increase in.leaf size is an
indication that expansion of the blades was greater in
the 40° than in the 50° F.N.T. In comparing the areas of
individual leaves in the long and the short photoperiodic
treatments, an average difference of 5.5 square inches
was found in the leaf areas in the 50° F.N.T. groups while
a difference of 5.9 square inches was found in the 40°

F.N.T. groups. These differences were both significant

14

was found between the average total leaf area per plant
in the short phot0period treatments in the 40 and 50°
F.N.T. As would be expected from the data presented in
Table II and Figures 4 and 5, highly significant differ-
6nces (at the 1 per cent level) were found in the total
leaf area per plant between the long and short photo-
peribd treatments for 25 weeks at the given temperatures.
At the 50° F.N.T. there was a difference of 260.8 square
inches, and a difference of 158.5 square inches at 40°
F.N.T.

The leaves on the plants in the 40° F.N.T. and long
days were found to be on the average 1.4 square inches
larger than the leaves on the plants in the 50° F.N.T. long
day treatment. Likewise the leaves on the plants in the
short days at 40° F.N.T. were found to be on the average
1 square inch.larger than the leaves on the plants in the
500 F.N.T. short day treatment. The differences between
temperatures were significant at the 5 per cent level for
the short day treatments and at the 1 per cent level for
the long day treatments. This increase in.leaf size is an
indication that expansion of the blades was greater in
the 40° than in the 50° F.N.T. In comparing the areas of
individual leaves in the long and the short photoperiodic
treatments, an average difference of 5.5 square inches
was found in the leaf areas in the 50° F.N.T. groups while
a difference of 5.9 square inches was found in the 40°

F.N.T. groups. These differences were both significant

a’ag ‘1‘ m a 9))
802900.
‘3. @655

I _.
,1, .
1‘ . . ‘
r - ' 1.“. .J.
9 ., d- g 'r
’ _ . -~'-'O‘ 'V ‘ 3%.? ‘. I .
‘ > | ‘ 'D‘ J. ‘ .
Ln ‘ _ ' , 1‘ _

.I a “it ‘
“'2" f ‘_.V
imam
’ . o,~4 “L

    
 
 

 

     
     

Fig. 6. Leaf blades and flowers from one violet
plant after 25 weeks of long days in a greenhouse
at 50° F. night temperature.

 

Fig. 7. Leaf blades and flowers from one violet
plantO after 25 weeks of short days in a greenhouse
at 50° F. night temperature.

15

at the l per cent level (Table II).

To further illustrate the difference in leaf size
in the different photoperiodic treatments, the leaves
from one plant in the 50° F.N.T., long photoperiodic
treatment are shown in Figure 6. The contrast in size of
these leaves compared to the leaves from a plant grown
in the short photoperiod at 50° F.N.T. (Figure 7) is

quite apparent.

Leaf Number. in average of 22.4 more leaves were
found on plants grown in the long photoperiod, 50° F.N.T.
than were found on those grown in the long photoperiod at
40° F.N.T. This difference was significant at the 1 per
cent level. No significant difference at the 5 per cent
level was found in leaf number between the short photo-
periodic treatments at the given temperatures (Table II).

Comparing the influence of photoperiod on the number
of leaves, it was found that a significantly greater number'
of leaves per plant (at the l per cent level) were produced
under the long photoperiod, than under the short photo-
period, 50° F.N.T. (Figures 6 and 7). The actual differ-
ence amounted to an average of 14.8 leaves. No signifi-
cant difference at the 5 per cent level was found in the
number of leaves produced per plant in the long and short
photoperiods at 40° F.N.T. (Table II).

Stoloniferous Growth. There was no development of

stolons at either temperature in the short phot0period.

16

Although.n0 actual measurements were made it was quite
apparent that stoloniferous growth was more rapid in the
50° than in the 40° F.N.T. in the long photoperiod.

General Influence 0f Temperature and Photoperiod. The
generally high significant differences in the vegetative
growth, found between the long and the short phot0periodic
treatments at both temperatures (Table II) shows that the
vegetative growth is more rapid in the long than in the
short photoperiod. The less vigorous growth in the short
photOperiod is further exemplified by the insignificant
differences, at the 5 per cent level, in the vegetative
growth.produced under the 8 hour photoperiod at the 40
and the 50° F.N.T. The significant increase in growth
under the long photoperiod in 50 compared to 40° F.N.T.
serves to show that also the higher temperature tends to
produce more vegetative growth.of Viggg;od0ratat Likewise
it follows_that the lower temperature tends to produce
less vegetative growth of this species.

It is important to note that although.both.the low
temperature and the short photoperiod used in this experi-
ment reduced vegetative growth, the differences in tempera-
ture did not influence the growth.as much as the differ-

'ences in the phot0periods used (Figures 4 and 5).

Influence of Photoperiodic Change. Photographs

(Figures 8 and 9) illustrate plants which were grown at

 

4'
= 4 0 LD .- to

Fig. 8. Violet plants grown at 40° F. night tem-
perature: Left, exposed to short days for 13 weeks
followed by long days for 12 weeks; Right, exposed
to long days for 13 weeks followed by short days
for 12 weeks; 511 plants grown concurrently in a
greenhouse.

‘ ‘“ '2?
. w weak LII-tn

\-

 

:"-I
Fig. 9. Violet plants grown at 50° F. night tem-
perature: Left, exposed to short days for 13 weeks
followed by long days for 12 weeks; Right, exposed
to long days for 13 weeks followed by short days
for 12 weeks; All plants grown concurrently in a
greenhouse.

17

the two temperatures and were moved from.the short to the
long photoperiod or from.the long to the short photo-
period 15 weeks after the start of the treatments. This
allowed them to grow for 12 weeks under the new photo-
period before the end of the experiment. It is interesting
to note that the plants in these figures on the left, moved
from.the short to the long phot0period at each.temperature,
have undergone a complete changeover and exhibit the
typical long day foliage-type. The leaves produced under
the short photoperiod prior to reversing the day length
have gradually turned yellow and died as the new, larger
leaves have grown and shaded them. The plants (right,
‘Figures 8 and 9), moved from a long to a short photoperiod,
had produced large leaves under the former long day treat-
ment. These leaves hang down around the edge of the pots.
Many of them have already turned yellow and have been re-
moved. The smaller, short photoperiodic foliage-type

will be noticed filling in the area around the crown of

the plant. ‘

Foliage produced under one photoperiod apparently
tended to die under the other photoperiodic treatment.
After changing the photoperiod, new leaves with a differ-
ent petiole length tended to force the older leaves aside.
The small leaves produced under short days were shaded
. by the large leaves produced under the long days and
gradually their source of light was reduced so that they

(e

TABLE III

INFLUENCE OF PHOTOPERIOD ON CHASMOGAMOUS
FLOWER PRODUCTION

GROUP II (40° SHORT DAYS)

 

 

 

Average Average Average
Number of number of stem.length flower
weeks after flowers in inches diameter
treatment produced in inches
was begun per plant
8 O O O
9 .02 5.25 1.00
10 .05 5.00 1.15
11 .05 5.88 1.15
12 .16 5.95 1.07
15 .12 4.55 .87
14 .12 5.81 .94
15 .27 4.59 ‘ 1.00
16 .56 4.58 1.04
17 .56 5.26 1.25
18 .88 5.14 1.07
19 1.15 5.18 1.26
20 .24 l 4.91 1.00
21 .50 5.91 .99
22 O O O
25 .06 5.75 1.12
24 .18 4.04 1.27
25 .58 2.95 .80
Total 4.90 66.11 16.92
Average .51 4.15 1.06

 

TABLE IV

INFLUENCE OF PHOTOPERIOD ON CHASMOGAMOUS
FLOWER PRODUCTION

GROUP Iv (50° SHORT DAYS)

 

 

 

Number of Average Average Average
weeks after number of stem length. ‘ flower
treatment flowers in inches diameter
was begun produced in inches
per plant

8 .07 2.67 1.00

9 .16 2.89 1.18

10 .14 2.65 1.17

11 .19 5.00 1.15

12 .49 4.21 1.17

15 .25 5.95 1.75

14 .55 4.61 ‘ 1.10

15 .55 4.80 1.11

16 .55 4.84 1.14

17 1.06 4.95 1.22

18 1.45 4.79 1.17

19 2.50 4.79 1.20

20 1.09. 4.46 1.17

21 1.15 4.51 1.08

22 .94 4.75 1.18

25 1.46 4.26 1.21

24 2.67 5.84 1.16

25 5.76 5.56 1.09

Total 18.55 75.27 21.21

Average (1.02 ,4.Q7_ 1.18.

TABLE V

INFLUENCE OF PHOTOPERIOD AND TEMPERATURE ON
CHASMOGAMOUS FLOWER PRODUCTION FOR PLANTS

MOVED FROM LONG PHOTOPERIOD TO SHORT PHOTOPERIOD

 

 

Number of Average Average Average
weeks after number of stem.1ength flower
treatment flowers in inches diameter
was begun produced in inches
per plant
GROUP IIA (40° F.N.T.)
21 O 0 O
22 0 O O
25 O 0 O
24 O O O
25 .7 5.11 .87
Total 5 weeks .7 5.11 .87
Average/week .14 5.11 .87
GROUP IVA (50° F.N.T.)
21 .8 2.06 .59
22 .9 2.26 .57
25 2.0 5.61 1.10
24 4.2 5.95 1.22
25 4.0 5.99 1.14
Total 5 weeks 11.9 15.85 4.62
Average/week 2.4 5.17 .92

 

TABLE VII
INFLUENCE OF PHOTOPERIOD ON CHASMOGAMOUS

FLOWER PRODUCTION. *
AVERAGES FROM SUMMARY OF TABLES II THROUGH V

- ( . . . _ ~ . ' . , .

 

 

 

Average Average Average
Treatment number of stem. flower
number flowers length . diameter
produced
per plant
II .55 4.15 1.06
IV .61 4.07 1.18
L.S.D. 005 .46 .53 .098
L.S.D. .01 .65. {.72 .15
IIA .14 5.11 .87
IVA 2.4 5.17 .92
IA .19 ' 5.87 .67

IIIA ‘ .36 _ 3.57 .67

 

*Data in treatments II and IV for average number of
flowers produced per plant is based only on data
up to the 21st week.

18

were unable to exist. Many of them.turned yellow and died.

Reproductive Growth

The flowers produced by the short photoperiod in
both temperature treatments were of the chasmogamous type.
The flowers produced by the long photoperiod in both
temperature treatments were of the cleistogamous type
(Figure 5). Madge (1929) obtained results similar to
these in her work at Royal Halloway College.

ChasmogamOus Flower ProductiOn. The data in Tables
_III and IV show flower production, flower diameter, and
peduncle length of the chasmogamous flowers produced.by
the short photOperiodic treatments. No significant differ-
ence at the 5 per cent level was found between the pro-
duction at the 50 and the 40° F.N.T. (Table VII).

The difference in the length of the peduncles pro-
duced under the two temperatures was not found to be
significant at the 5 per cent level. The flowers pro-
duced under the 50° F.N.T. and short photoperiod were on
the average 0.12 inches larger in diameter than were the
flowers produced under the 40° F.N.T. This was signifi~
cant at the 5 per cent level (Table VII).

The production of chasmogamous flowers in the short
photoperiod, 40° F.N.T. treatment ceased in the 21st week.
Two weeks later on April 24th.the productiOn of chasmo-

19

gamous flowers was resumed. During the 22nd week a con-
siderable number of cleistogamous flowers were Observed

on these plants and they continued to be produced through.
the 24th.week. An attempt was made to find a physiological
explanation for the change from the production of chasmo-
gamous to cleistogamous flowers and back to chasmogamous
flower production in less than four weeks.

The causal factor involved in this change in flower
type was obviously one of photoperiod. It may be that the
cloth used to shade the plants in the 40° F.N.T. house was
not of sufficient density to completely shut out the more
intense light of the early spring months. At the date of
repotting in the 18th week, a larger black cloth.was re-
quired to completely cover the plants. This was of double
thickness and may have been the cause of changing the
plants into a short day behavior, so that they again
produced chasmogamous flowers five weeks later and contin-
ued to increase the production during the remainder of
the investigation. It is of interest to note that 20
plants whiCh.were retained under short photoperiod after
the 25th week, continued to produce chasmogamous flowers
in large quantities until the plants were discarded in the
middle of June.

Cleistogamous Flower Production. Cleistogamous
flowers were produced on plants grown under long days at

both the 40 and 50° F.N.T. throughout the investigation.

20

Reversal bf Photoperiod. The production of chasmo-
gamous flowers by those plants moved from long to short
days the l5th.week is shown in Table V. Production of
chasmogamous flowers began 8 weeks after the plants were
exposed to short days in the 50° F.N.T. (2lst week). The
flowers produced prior to the 10th week after the date of
starting the short photoperiodic treatment were not of
saleable quality. The flowers were small; the peduncles
were short. The diameter of the flowers was 0.58 inches
compared to an average of 1.06 inches for the 25 week
period. The peduncles were 2.16 inches contrasted to
4.15 inches on the average for the 25 week period.

In the 40° F.N.T. treatment, those plants moved
from.the long to the short photoperiod after 15 weeks
did not produce any chasmogamous flpwers until 12 weeks
after the date of starting the short photoperiodic treat-
ment. It is likely that the cloth used at the 400 F.N.T.
prior to the 18th week was inefficient at the higher
light intensities Of that date and the production of chas-
mogamous flowers in the 400 F.N.T. and short phbtoperiod
was undoubtedly unduly delayed.

Cleistogamous flower production ceased after 5 weeks
on all plants moved from.the long to the short photoperiod
in the 50° F.N.T. during the l5th.week. Those plants
exposed to the short photoperiodic treatment in the 40°
F.N.T., however, continued cleistogamous flower production

for approximately 10 weeks. This was probably caused by

21

the inefficient exclusion of light prior to the 18th week.

The plants which.were moved from a short to a long
photoperiod during the 13th.week continued to produce
chasmogamous flowers for a period of 5 weeks (Table VI).
The slight difference in the extended period of production
of chasmogamous flowers on plants in the two different
night temperatures shows that the temperature had little
effect upon the rate of the development of the flower
types after the type had been differentiated.

The production of cleistogamous flowers on those
plants moved from.a short to a long photoperiod in the 15th

week began 9 weeks after the date of moving.

Influence of Leaf Type on Flower Type. Six weeks
after efficient shading was applied to the 40° F.N.T. and
short photoperiodic treatment the chasmogamous flowers were
again produced, leaving only one week during which.the
chasmogamous flowers were not produced (Table III). Yet
it required 10 weeks after the plants were moved from a
long to a short photoperiodic treatment at 50° F.N.T. for
good quality chasmogamous flowers to be produced (Table V).
It seems reasonable to draw the conclusion from these two
observations, that for chasmogamous flowers to be produced,
the short photoperiodic foliage-type must first be present
to produce a stimulus, the cause of chasmogamous flower buds.
It required four more weeks for plants to produce chasmo-

gamous flowers when they were moved from.a long to a short

22

photoperiod than when all buds were removed from the
plants which were abundant in the short day foliage-type
and were continued in a short photoperiod. For plants
which.were moved to the short photoperiod to produce chas-
mogamous flowers, they first had to produce the short day
type of foliage in order to produce the chasmogamous
flowering stimulus.

Similarly it seems likely that the long day type of
leaves are necessary to produce the stimulus which.eauses
the formation of cleistogamous flowers. This is shown by
a similar period of nine weeks which.passed before the
production of cleistogamous flowers began on those plants
moved from the short to the long photoperiod. The con-
ception is further supported'by the fact that the plants
moved from the long to the short photoperiod in the 50°
F.N.T. ceased cleistogamous flower production after a
period of five weeks.

It is believed that the results obtained in the 40°
F.N.T. short photoperiodic treatment did not follow the
results obtained in the other treatments because of the
ineffective cloth.used for shading the plants. This
meant that the plants had been exposed to a longer photo-
period than was intended. This photoperiod may not have
been long enough to cause the dissipation of the short
photoperiodic type of leaves. As soon as the short photo-

period was returned the leaves were already present to

25

produce the stimulus which.might cause the production of
chasmogamous flowers. The continued production of cleisto-
gamous flowers by the plants moved to this treatment from
the long photoperiod for 10 weeks after the date of moving
(13th week), was also apparently caused by the accidental
extension of the photoperiod prior to the 18th.week. This
extension was sufficient to cause the long day type of
foliage to produce the stimulus which.may have been
sufficient to cause the cleistogamous flower production.
On the basis of this theory it would appear to re-
quire five weeks for a flower of 23315.0dOrata to develop
after it has been initiated. This is similar to the
findings of Garner and.Allard (1920) who concluded that
it took about one month to produce chasmogamous flowers.
In Garner and Allard's work no mention was made of the I
type of foliage on the plants at the beginning of the
treatment. In addition to the fiVe week period required
for the flower development an additional four week period
seems to be essential for the plants to produce the type
of leaf which.may be the source of the flower stimulus.

Application to Greenhouse Operation. Commercial
flower production will take place only under a short photo-
period. It requires 10 weeks of this photoperiod to pro-
duce saleable flowers when the plants are grown at a 500
F.N.T. The flowers are larger and there is a greater
leaf area per plant when they are grown at 50 rather than

24

at 40° F.N.T.

A greenhouse Operator desiring to keep his planting
of violets in good production for the late spring markets,
should control the photoperiod received by the plants at
8 hours and the temperature at 500 F.N.T. It appears of
little value to supply a long photoperiod to obtain vigorous
growth, since under the shorter photoperiod, the long day
foliage type tends to dissipate. (Cleistogamous flowers
would be initiated in the axils of the long day type of
leaves. Unless seed production was desired, unnecessary
utilization of carbohydrates would take place.

By furnishing the large well grown plants with an
8 hour photoperiod and a 50° F.N.T. for 10 weeks prior
to the time they are planted in the greenhouse in the
fall, the plants should produce good quality flowers
almost immediately and increase the production per square

foot of greenhouse bench.

SUMMARY

Plants of 23215.0d0rata var. Fries Favorite were
planted in sterilized soil in 4 inch.pots. On November
9, 1950, the following treatments were begun: I. 43 plants
exposed to a 40° F. night temperature and a 16 hour photo-
period; II. 43 plants exposed to a 40° F. night temperature
and an 8 hour photoperiod; III. 43 plants exposed to a 50°
F. night temperature and a 16 hour photoperiod; and IV. 4:5
plants exposed to a 50° F. night temperature and an 8 hour
photoperiod. During the 13th.week of the experiment, 10
plants were selected at random.from each treatment and
moved to the Opposite photoperiod in the same temperature
at which.they had been growing.

Weekly records were made of number and size of chasmo-
gamous flofiers produced between the 8th.and 25th week of
treatment. it the end of the 25th week, on May a, 1951,

a comparison of vegetative growth.was made by measuring
the area of all of the leaves from.ten plants in each
treatment.

Results indicated that a photoperiod of 16 hours
tended to be more favorable for vegetative growth.of
Eiglg_0dorata‘than a photoperiod of 8 hours. A 50° F.
night temperature also tended to be more favorable for

26

vegetative growth than a 40° F. night temperature. Photo-
period in this investigation was more effective than
temperature in reducing or increasing vegetative growth.

The short photoperiod of 8 hours favored the pro-
duction of chasmogamous flowers, while the long photoperiod
of 16 hours favored the production of cleistogamous
flowers. A 50° F. night temperature produced larger chas-
mogamous flowers than did a 40° F. night temperature.

From.the date of beginning the short photOperiodic
treatment, it required between 8 and 10 weeks to produce
chasmogamous flowers at the 50° F. night temperature,
providing the short day type of foliage was not present
on the plant at the beginning of the treatment. Plants
moved from a short to a long day continued chasmogamous
flower production for a period of approximately five weeks
at either 40 or 50° F. night temperature.

The period of time required for cleistogamous flower
production to begin when the plants were moved from short
to long days was approximately 9 weeks. The extended
period of production of cleistogamous flowers after the
plants were removed from.the short day length was 5 weeks.

It is suggested that the stimulus causing the pro-
duction of the two different flower types in.22213'odorata
is produced by a foliage-type characteristic of the respec-
tive day lengths found to favor production of the flower

types. Recommendations are made for commercial growers of

violets to control the flowering period by the use of
regulated day length.and temperature.

The text is augmented by 9 illustrations and VII
tables.

27

BIBLIOGRAPHY

Allard, H. A. and Garner, W. W.

1940. Further observations on the response of various
species of plants to length of day. U. 3.
Dept. Agr. Tech. Bul. 727:1-64.

Bergdolt, E.

1952. Morphologische und physiologische untersuche
ungen uber Viglg. zugleich ein beitrag zur
losung des prOblems der'kleistogamie. Botan-
ische Abhandlungen. Herausg. von K. Goebel
Heft. 20:1-120, fig. 1-67.

Bradley, J.
1901. Violets. Florists Exchange. 1314:388-389.
Chouard, P.

1947. The effect of the photoperiod and thermoperiod
on the various flower types of violets with
special reference to 23215 93-3373. and M
gzlvestris. Comptea Rendus des Seances
Academic des Sciences. 224:1523-25.

Garner, W. W. and Allard, H. A.

1920. Effect of the relative length of day and night
and other factors of the environment on
growth and reproduction in plants. J. Agr.
Res. 18:555-601.

29

Gorczynski, T.

1952. Z badan nad kleistogamja III. Dymorfizm
kiiatowy u.fjolka wonnego pelndkwiatowego
(Egglg'odorata fl pleno hort). (Studies on
cleistogamy III. Floral dimorphism in the
double violet (X, odorata fl. pleno hort).
(Fr. resume) Acta. Soc. Bot. Poloniae 9%:
115-150, fig. 1-4, pl. 1.

Hamner, K. C. and Bonner J.

 

1958. PhotOperiodiSm.in relation to hormones as
factors in floral initiation and development.
'Bot. Gaz. 100:588-451.
Madge, Margaret P.
1929. Spermatogenesis and fertilization in cleisto-
gamous fl. of Viglg_odorata var. praecox.
Ann. Bot. (London). 43:545-577, fig. 1-12,
pl. 1.
Murneek, A. E.
1940. Length of day and temperature effects in
Rudbeckia. Bot. Gaz. 102:269-279.
Post, Kenneth.
1949. Florist CrOp Production and Marketing. 84l-846._
Roberts, R. H. and Struckmeyer, B. E.
1959. Further studies of the effects of temperature
'and other environmental factors upon the

photoperiodic responses of plants. J. Agr.

30

Res. 59:699-709.
Steinburg, R. A. and Garner W. W.

1956. Response of certain plants to length of day
and temperature under controlled conditions.
J. Agr. Res. 52:945-960.

Theron,.A.

1959. Recherches morphologiques et cytologiques sur
les flours de Viglg.odorata. Rev. Cyt. et
CytOphysiol. Veg. 41:101-118, pl. 1-2.

Weste, G.

1951. Cleistogamy in.23215 Riviniana with especial
reference to its cytological aspects. Ann.
Bot. 44:87-109, fig. 1-4.