By

JASPER GUY WOODROOF

A THESIS
Presented to the Graduate School of Michigan State College of Agri­
culture and Applied Science in Partial Fulfillment of Require­
ments for the Degree of Doctor of Philosophy

Horticulture Department
East Lansing, Michigan
1930

ProQuest Number: 10008498

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S T U D IE S O F T H E S T A M IN A T E IN F L O R E S C E N C E A N D
P O L L E N O F H IC O R IA P E C A N 1
By J. G.

W oodroof 2

A ss o c ia te H o r tic u ltu r is t, G eorgia A g r ic u ltu r a l E x p e r im e n t S ta tio n

IN T R O D U C T IO N

F rom th e producer's stan d p o in t one of the m ost im p o rtan t lim iting
factors to profits in pecan culture is low yields. These m ay be due
to any one or to a com bination of several factors, such as the failure
of the trees to differentiate flowers, more especially pistillate flowers,
poor pollen, unfavorable w eather during the flowering season, or
insect or disease a tta c k upon flowers or developing fruits. C on­
siderable stu d y has been devoted to some of these questions. L ittle,
however, has been recorded regarding the developm ent of pollen in
th e pecan, though pollen deficiencies are known to be responsible
for u n satisfactory fru it setting in certain varieties of apples, pears,
plum s, grapes, and m any other fruits. I t therefore appeared to the
w riter th a t a stu d y of the m orphology of the stam in ate inflorescence
and physiology of the pollen would throw some light on practical
questions of pollination.
R EV IE W OF L IT E R A T U R E

U nfruitfulness of the pecan (Hicoria pecan B rit.) is associated
more closely w ith the initiation and developm ent of pistillate th an
of stam in ate flowers, and it is therefore logical th a t the pistillate
flowers should have been studied first. Studies of the m orphology
of pistillate flowers of pecans have been m ade by W oodroof {27,
28),3 S h u h art {21), and Isbell {12), and the results have shown
close agreem ent as to the time and m anner of developm ent. S tam i­
n ate flowers have received secondary attention, b u t fragm entary
descriptions have appeared in a few reports {23, 26, 12, 27, 28).
S tuckey {23) studied the developm ent of stam inate flowers of 33
varieties of pecans. H e divided the varieties into two groups on
the basis of th e length and size of the catkins, length of bracts, and
tim e of shedding pollen. W oodroof {26, 27) found th a t catkins were
differentiated in lateral buds throughout the growing season of
1 R e c e iv e d for p u b lic a tio n S ep t. 19, 1929; issu e d .Tune, 1930. P r e sen te d to th e fa c u lty of M ic h ig a n S ta te
C o lleg e o f A g r ic u ltu r e a n d A p p lie d S cien ce, in p a rtia l fu lfillm e n t of th e r e q u ire m e n ts for th e d egree of
d o cto r of p h ilo s o p h y a n d p u b lish ed w ith th e a p p r o v a l of th e d irector of th e G eorgia A g r ic u ltu r a l E x p e r i­
m e n t S ta tio n as p ap er N o , 31, J o u rn a l Series.
2 In th e in v e stig a tio n s h ere reported N a o m i C. W o o d ro o f, of th e D e p a r tm e n t of B o t a n y , a n d J. E . B a ile y ,
o f th e D ep artm en t, of H o rticu ltu r e , o f th e Georgia. A g r ic u ltu r a l E x p e r im e n t S ta tio n , a id ed in co llectin g
field d a ta and in p reparin g m a teria l for la b o r a to r y s tu d ie s . O tis W o o d a rd , of th e G eorgia C o a sta l P la in
E x p e r im e n t S ta tio n , fu rn ish ed a p a rt of th e d a ta for T a b le 5; C . F. W illia m s , of th e N o r th C a ro lin a A g ri­
c u ltu r a l E x p e r im e n t S ta tio n , a n d R . M . M id d le to n , of th e G eorgia s ta tio n , fu rn ish ed a part of th e data
for th e sa m e (ab le. M e m b e r s o f th e D e p a r tm e n t of H o rticu ltu r e of M ic h ig a n S ta le C o lleg e offered su g ­
g e stio n s in th e p la n n in g of th e w ork a n d cr itic iz ed th e m a n u sc rip t; a n d W . C . D u tt o n a id ed in m a k in g
p h o to m ic r o g r a p h s ,
R eferen ce is m a d e b y n u m b e r (ita lic ) to “ L iter a tu r e c it e d ,” p. 1103.
J o u r n a l of A g r ic u ltu r a l R esea rch ,
W a sh in g to n , D . C .
109031—30

1

V o l. 40, N o . 12
J u n e 15, 1930
K e y N o . Ga.-G

(105 9 )

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Jo u rn a l of A gricultural Research

VoJ. 40, N o . 12

th e y e a r prio r to th e shedding of pollen. H e re p o rted m easurem ents
of catk in s of th e tw o groups of v arieties during th e w inter stage and
described th e m eth o d of shedding b u d scales th e following spring.
Isbell (12) published 13 photom icrographs illu stra tin g progressive
stages of c a tk in d evelopm ent during th e sum m er.
H iggins (JO) described a disease (Microstroma juglandis (B ereng.)
Sacc., var. robustum, n. v ar.) of pecan catkins th a t appeared on all
of th e v arieties observed and som etim es d estroyed o n e-th ird of th e
pollen. T h e tissues of th e c a tk in wTere n o t killed o u trig h t, b u t the
pollen grains degenerated, often leaving collapsed walls.
T his
disease is com m on in th e orchard in w hich th e p resen t stu d ies were
m ade, b u t care was ta k e n to avoid using diseased m aterial.
S ch u ster (18) s ta te d th a t th e am o u n t of pollen produced by filberts
in Oregon varies from season to season and is influenced by m any
factors. M an y varieties produce a h eav y crop of sta m in a te and
p istillate flowers one year, and a light crop of b o th th e following year.
V alleau (24), w orking w ith straw berries, D orsey (8) w ith plum s,
K now lton (15) w ith th e J. H . H ale peach, an d Asarni (3) w ith
Shanghai peach, re p o rt t h a t th e first abnorm al developm ent in
pollen was seen a t th e tim e of lib eratio n from th e te tra d w all; th ere­
afte r m icrospores were found in various stages of abortion. S hoem aker
(19, 20) found lagging chrom osom es in th e h etero ty p ic division,
giving rise to abnorm al pollen in th e apple and cherry.
T he germ ination of pollen on artificial m edia has been u n sa tis­
factorily accom plished w ith pollen of m an y p lan ts. W ood 4 found
th a t alm ond an d w aln u t pollen did n o t germ inate well on sugar-agar
m edia, and concluded th a t th ere was no satisfac to ry lab o ra to ry
m ethod of ascertaining the v iab ility of pollen of various varieties.
A nthony and H a rla n (2) a tte m p te d to duplicate n a tu ra l conditions
for g erm inating barley pollen by placing a piece of m esophyll from
th e leaf of the garden pea in the cell to supply w ater. T h e cell was
covered w ith a cover glass and placed in th e open to allow th e con­
d ensation of m oisture on th e pollen grains. G erm ination was accom ­
plished w ith b o th m esophyll an d drops of w a te r for hum idifiers.
B eau m o n t and K n ig h t (5) and K now lton (15) a tte m p te d to approach
n a tu ra l conditions for germ inating apple pollen by adding stigm as
of th e sam e or different varieties to a hanging drop a t th e sam e tim e
the pollen was added. T h ey concluded th a t fu rth e r im p ro v em en t
of th e m ethod of germ ination was necessary to produce pollen-tube
len g th equal to th a t produced un d er n a tu ra l conditions. L idforss
(17) rep o rted th a t artificial m edia for g erm inating pollen m u st co n tain
n o t only the essential n u tritiv e substances b u t th a t it m u st n o t contain
su b stan ces w hich p rev en t grow th, especially m ineral salts, as calcium .
T h e m ost satisfacto ry results, from pollen-germ ination tests in
general, have been o b tain ed by using from 1 to 2 per ce n t agar or
gelatin and 5 to 20 per cent sucrose in the m edia. H o w le tt (11) used
10 p er cent sucrose and 2 per cent agar; B eau m o n t and K n ig h t (d)
used 5 p er cent sucrose and 1 p er cent gelatin for g erm in atin g apple
pollen; B ooth (6‘) used 15 per cent sucrose an d l l/ 2 p er cen t g elatin for
g erm in atin g plum pollen and 10 per cent sucrose and 5 p er cen t g elatin
for g erm inating cherry pollen; S chuster (18) o b tain ed b est germ in atio n
of filbert pollen in 12 to 15 per cent sucrose b u t observed b u rstin g of
* W o o d , M . N . p o l l e n s t u d ie s o f a l m o n d a n d w a l n u t .
C a lifo r n ia .)

1917.

( M a s t e r ’s t h e s is .

U n iv e r s it y of

June is, 1930 Stam inate Inflorescence and Pollen of Hicoria pecan

1061

pollen grains and tubes; A uchter (4) germ inated apple pollen in
distilled w ater; and K n ig h t (14) increased apple-pollen germ ination
b y adding a trace of asparagine to the m edium .
V alleau (24) determ ined the percentage of defective grains in
straw b erry pollen and reported th a t—
lactic acid has the advantage over water or alcohol for this purpose as it is not
volatile and seldom, if ever, breaks the pollen grains through osmotic pressure.
It readily enters and expands the normal grains, while it leaves the aborted grains
collapsed.

D orsey (8) studied plum pollen and reported th a t the ex ten t of
pollen ab o rtio n in selected form s was determ ined p a rtly from m ounts
in lactic acid and p a rtly from stained sections. In S hoem aker’s (19)
w ork w ith apples lactic acid was em ployed to afford a liquid m edium
w hich would p rev en t bursting and germ ination of the pollen grains.
B eau m o n t and K n ig h t (5) hand-pollinated apple blossoms, and after
the pollen h ad germ inated and p en e trated the stigm as the la tte r were
flatten ed on a cover glass and m ounted in lactic acid which killed and
fixed the pollen tube. Snow (22) used lactic acid in a sim ilar m anner
in stu d y in g the pollen of stocks. F lo rin ’s (9) germ ination tests
closely checked w ith the lactic acid exam inations of apple and pear
pollen.
M E TH O D S

M a te ria l for m orphological studies was tak en from an orchard of
28 varieties a t the G eorgia E xperim ent S tation. T he location is
a b o u t 150 miles n o rth of the center of pecan production in Georgia.
M o st of the trees are 20 years old and have had uniform culture.
D a ta on pollen dissem ination were tak en in com m ercial orahards near
B arnesville, Ga.
In general, th e m ethods of collecting, killing, fixing, em bedding,
sectioning, and staining m aterial for m icroscopical studies were the
sam e as those described in previous reports (27, 28, 31).
T he Alley and F rotscher varieties were chosen as typical of Groups
1 and 2, respectively, according to S tu c k e y ’s classification (23). O ther
varieties were repeatedly used to verify results. J u e l’s fixative 5
and picro-sulphurous acid 6 were used as killing and fixing agents, the
la tte r giving the b e tte r results. M aterial was taken a t 15-day
in terv als th ro u g h o u t the year from each variety, alternating the
fixatives. N orm al buds were selected from representative shoots,
and norm al flowers were tak en from catkins typical of the variety.
F ro m the m other-cell stage until pollen shedding, catkins of the
S tu a rt v arie ty were collected daily; and during the reduction division,
m aterial of the F rotscher and S tu a rt varieties was collected a t 3-hour
in terv als. B uds collected during the actively growing season wrere sec­
tioned 5 m icrons in thickness. T he hairy n atu re of w inter buds ren­
dered it difficult to section them sufficiently thin for cellular studies.
A m odification of the sm ear m ethod, as described by K aufm ann
(13), was used to determ ine the num ber of tetra d s per an th er and the
n u m b er of pollen grains per pollen sac. An an th er in the te tra d stage
w'as placed in a drop of w ater on a slide and thoroughly m acerated w ith
a needle. T he tetra d s separated from the an th er wmll and floated
in d ep en d en tly in the m edium . A fter the fragm ents of the an th er
* J u e l ’s fix a tiv e : Z n C h , 2 g m .; a c e tic a cid , 2 c. c.; a lco h o l, 95 per c e n t, 50 c. c.; d is tille d H 2O,_50 c. c.
* P ic r o -su lp h u r o u s acid : S u lp h u r o u s a c id , 6 per c e n t, 10 c. c.; p icric a c id , 1X
A gm .; a lco h o l, 75 per c e n t,

11)62

Journal of A gricultural Research

V ol. 40, N o . 12

wail were rem oved the te tra d s were stain ed w ith eosin, covered w ith
a cover glass, an d exam ined u n d er th e high pow er of th e m icroscope.
D issem in atio n of pollen w as stu d ied by ca tch in g pollen from th e
a ir on slides greased w ith vaseline, a m eth o d sim ilar to th a t used by
W au g h {25) for catch in g plum , pear, an d apple pollen. Tw o y a rd ­
sticks w rap p ed w ith cheesecloth an d loosely b olted to g e th e r m ade a
convenient holder for 12 slides. A b o u t tw o -th ird s of th e length of
each slide was exposed, th e re m a in d er being held firm ly betw een th e
y ardsticks. T h ree series of slides w ere m o u n ted on a slender pole,

F ir , c u e 1. — A, P o le 30 feet h ig h s u p p o r te d b y g u y w ir e s to w h ic h w ere a t ta c h e d th r ee se rie s of
g rea sed slid e s for c a tc h in g p o l l e n fro m th e air; H, v ia ls c o n t a in in g w a te r a n d c a lc iu m c h lo r id e ,
in w h ic h w ere p la c ed s m a lle r v ia ls c o n t a in in g p e c a n p o lle n w h ic h w a s k e p t “ m o is t " a n d " d r y ’’
r e s p e c t iv e ly ; C , c ells f o r g e r m in a tin g p o lle n . A r r o w s in e a c h ca se in d ic a te p o s itio n of th e p o lle n

one series each 10, 20, and 30 feet above th e ground. T h e slides
were set on th e leew ard side of th e trees, a t a 45° angle w ith the
ground, the greased face of th e slide being tu rn e d to w ard th e pollenshedding trees. T he slides were changed by low ering an d raising
the pole w ith th ree guy wires. (Fig. 1, A.)
Pecan pollen grains on th e greased slides were identified and
co un ted un d er the low-power objective of th e m icroscope. A fter
the area ol th e m icroscopical lield was calculated, th e n u m b e r of
g rains in 200 fields were counted, averaged, an d calcu lated to the
n um ber of grains per square centim eter.

June is, 1930

Stam inate Inflorescence and Pollen of Hicoria pecan

1063

T h e w ind velocity was determ ined by the use of a R obinson cup
an em o m eter w ith electric connections and a buzzer which indicated
th e n u m b er of miles per hour. T he relative h um idity was determ ined
by th e use of a sta tio n a ry hygrom eter placed in the orchard.

M ETRIC

F ig u r e 2 .— A . .M icrospore p rin t m a d e from a p eca n c a tk in of G ro u p 1 s h o w in g th e ca se w ith w h ic h
pec m p o lle n m a y be c o lle c te d in q u a n tity ; If. p h o to m icrograph of lo n g itu d in a l s e c tio n of A lle y
v a r ie t y a n th e r w h ile in th e m o th e r -c ell s ta g e on A p ril 1; in so m e e a ses th ere se em to he ro w s of
m o th e r c e lls

Pollen for germ ination tests was obtained from ripe anthers which
were allowed to dehisce in the laboratory. (Fig. 2.) In this way
th e tim e of dehiscence could be determ ined to w ithin two hours,
('ells for germ inating pollen were m ade by shellacking six hard

1064

Jour nal of A gricultural Research

Vol. 40, N o . 12

ru b b e r rings, 15 m m . in d iam eter an d 10 m m . high, to glass slides
2 inches w ide an d 3 inches long. W a te r to su p p ly m o istu re for
g erm in atio n w as placed in th e b o tto m of each cell. A drop of sterile
g erm in atin g m edium was placed on a cover glass while h o t an d allowed
to solidify. T h e pollen was d u sted on th e m edium an d th e cover
glass was in v erte d an d sealed on th e cell w ith vaseline. E x a m in a ­
tions were m ade a t in terv a ls u n d e r low pow er w ith o u t d istu rb in g the
cell. (Fig. 1, C.)
D ry an d m oist storage conditions w ere provided by placing cal­
cium chloride a n d w ater, respectively, in tw o 50 c. c. vials. A
10 c. c. vial co n taining pollen was placed in each 50 c. c. vial a n d the
la tte r was corked. (Fig. 1, B .) A du p licate series w as set up for
each v a rie ty an d tem p eratu re. E lectric ovens pro v id ed tem pera-

F ig u r e 3 .— A, T w ig from .Stuart p e c a n tree w h ic h bore 3 p o u n d s of n u t s la st y ea r; B , t w ig fro m
-M obile treo w h ic h bore 29 p o u n d s of n u t s la st y ea r. T h is tree a n d t h a t in A are b o th 12 y e a r s
o ld an d h a v e r e c e iv e d th e sa m e fer tilize r arid c u ltu r a l t r e a t m e n ts sin c e b e in g se t in th e o rch a rd .
C , T w ig from -M cA lister v a r ie t y , a s u p p o s e d h y b r id b e t w e e n H ic o ria p e c a n a n d C 'anja alba,
w h ic h has a c a tk in p r o d u c in g h a b it lik e C. a lba, i. e ., o n ly th e t e r m in a l b u d p r o d u c e s c a tk in s

tu res co n stan t a t 32°, 25°, 23°, an d 22° C .; and a re frig erato r p ro ­
vided a tem p eratu re of 5° C.
M o u n tin g pollen in lactic acid for m icroscopical d eterm in a tio n of
the percen tag e of defective grains seems a m ore reliable m eth o d
th a n g erm in atin g it on artificial m edia. Tw o drops of 90 per cen t
lactic acid placed on a slide w ith a sm all a m o u n t of pollen an d covered
w ith a cover glass render th e grains containing a norm al a m o u n t of
p rotoplasm d istin ct from those containing less th a n th e n o rm a l
am o u n t. A bout three m inutes are req u ired for com plete p e n e tr a ­
tion; afte r three hours the grains becom e bleached an d d ifferen tiatio n
of defective and norm al grains is uncertain. F resh m ounts an d high
m agnification are necessary for one to m ake reliable co u n ts by th is
m ethod.

June i5, 1930 Stam inate Inflorescence and Pollen of Hicoria pecan

1065

P R E S E N T A T IO N OF E X P E R IM E N T A L D ATA

T he lateral buds of a growing shoot on a bearing pecan tree differ­
en tiate ca tk in prim ordia by the tim e the subtending leaf is one-tenth
grown {26, 27). D ifferentiation begins about two weeks after active
grow th s ta rts in th e spring (April 15) and continues throughout the
grow ing season. In the pecan, catkins are alw ays produced in lateral,
axillary buds (figs. 3, 4), and the num ber of catkin prim ordia formed
is in pro p o rtio n to th e n u m ber of leaves produced on th a t shoot.
N orm ally th ere are two groups of three catkins each produced at
each node. In o th er native hickories {Carya alba, C. ovalis, C.
glabra) th e catkins are produced in the term inal bud. (Fig. 3, C.)

F i g u r e 4.— A, T w ig fro m M o b ile tree w h ic h bore 58 p o u n d s of n u t s la st y ea r; tree from v a r ie ty of
G ro u p 1; B , t w ig from A lle y tree w h ic h bore 34 p o u n d s o f n u t s la st year; tree from v a r ie t y of G ro u p
1; C , tw ig from F r o tsc h e r v a r ie t y w h ic h bore 100 p o u n d s of n u ts la st year; tree from v a r ie ty of
G ro u p 2; D , t w ig from S tu a r t tre e w h ic h bore n o n u ts la st year; tree from v a r ie t y of G ro u p 2. A ll
of th e se trees are 20 yea rs o ld a n d h a v e r e ce iv e d th e sa m e fertilizer a n d c u ltu r a l tr e a tm e n ts sin ce
b e in g s e t. A r r o w in d ic a te s p o in t of a b sc issio n of th e c a tk in b u d s on A p ril 'J

T he ch aracteristics of th e buds and inclosed catkin prim ordia
have been previously described by the w riter {26). T he central
catk in is form ed and develops som ew hat in advance of the catkins
borne on eith er side, and ultim ately reaches a g reater length at
m a tu rity . (Figs. 5, 6, 4.)
T H E TW O G R O U P S O F V A R IE T IE S

S tu c k ey ’s {23) description of th e two groups of varieties was based
on ch aracteristics of the catkins a t the tim e of pollen shedding. The
w riter {26) found th a t th e catkin prim ordia of G roup 1 have a greater
diam eter an d lesser length th a n those of G roup 2 in both O ctober
an d J a n u a ry {26). Such m easurem ents aid in differentiating the

Journal of A gricultural Research

1066

V o l. 40, N o . 12

i-A -i

F ig u r e 5

- C a t k in s o f p e c a n v a r ie tie s in G ro u p 1: A , A lle y ; B , J er o m e ; C , M o b ile ; D , M o b ile fro m
n o n v ig o r o u s b u d (0.57 n a tu r a l size)

its I

-A

v* & £
¥■ %

■ ^

A ik J ^

M

|I
'<V

OT'

V
Cat k in s o f p e c a n v a r ie tie s in G r o u p 2; A , V a n D e m a n ; I I . F r o tsc h e r ; ( \ T e c h o
The
J rorsenior a n d 'I ech o v a r ie tie s h a v e a lar^e n u m b e r of a b o r te d flo w ers n ea r th e b a se of th e c lu ste r
i.O.of n a tu r a l size;

F i j r V K K 6. —

June is, 1930 Staminate Inflorescence and Pollen of Hicoria pecan

1067

two groups, b u t as diam eter an d length v ary w ith th e vigor of th e
tree, th ey can n o t be depended upon solely.
T h ere seem s to be no difference betw een th e m ode of differentiation
an d ty p e of grow th of th e catkins of the two groups of varieties
during th e spring an d sum m er, b u t a m arked difference is evident
by early fall.

F

7 — P r im o r d ia of sta m in a te inflorescence: B , I n itia l fo rm a tio n
o f a gro u p o f th ree c a tk in s w it h in a sin g le b u d sca le, M a y 15; A ,
s in g le in flo rescen ce six w e e k s later: a, b u d scale; b, p rim o r d iu m
o f an in d iv id u a l flow er; c, in it ia l fo rm a tio n of v a sc u la r b u n d le s.
F r o tsc h e r v a r ie ty . X 181

ig u r e

In d iv id u al flower prim ordia develop as lateral “ b u m p s” on the
axis of th e ca tk in prim ordium , beginning a t the base and progress­
ing to w ard the term inus. (Fig. 7.) In G roup 1 flower prim ordia
continue to form a t the term inus, while th e older ones near the base
differentiate an thers by early fall. B y the tim e grow th practically
ceases in the fall anthers are distinguishable along the entire length
of th e axis. (Figs. 8 and 9 and T able 1.) T hus the w inter stage of
G roup 1 shows com plete differentiation of anthers and bracts.
109031 — 30—

2

Journal of Agricultural Research

1068

F

V o l. 40, N o . 12

8.— A , I n d iv id u a l flo w er p r im o r d iu m s h o w in g s p e c ia liz a tio n o f c e lls b u t n o d iffe r e n tia tio n
of floral organs; e n la r g e m e n t of F ig u r e 7, X 1040; B , A lle y v a r ie t y o n M a r c h 15 s h o w in g floral
o r g a n s w e ll d iffe r e n tia te d ; X 114; C , F r o tsc h e r v a r ie t y o n M aT ch 15 s h o w in g v e r y e a r ly s ta g e
in d iffe r e n tia tio n o f floral organs; X 114; D , F r o tsc h e r v a r ie t y o n A p r il 1 s h o w in g floral o rg a n s
in s a m e sta g e as A lle y o n M a r c h 15; X 114

ig u r e

F igure 9.— A, Photom icrograph of lo n g itu d in a l section of two lobes of an anther showing mother cells just before rounding up; B, photom icrograph cross section of one lobe of an a n th e r
showing mother cells undergoing reduction division; C, photom icrograph cross section of one lobe of anther showing tapetum cells disin teg ra tin g , and tetrads within the m o th er
cell walls; one tetrad is elon gated, indicating a b n o r m a lity

June is, mo Stam inate Inflorescence and Pollen oj Hicoria pecan
1069

1070
T a b le

Journal of Agricultural Research

v o i. 40, n o . 12

1 .— S ta g e s of d e ve lo p m e n t of pollen o f p e ca n v a rities in G ro u p s 1 a n d 2

G ro u p s at s ta g e of d e v e lo p m e n t m e n tio n e d at t im e in d ic a te d

S ta g e of d e v e lo p m e n t

j

I

* g ® 3

M arch

A p ril

M a;

10 20 1 ! 10 | 21) 1 ! 10
D if fe r e n t ia lio n o f in f l o r e s c e n c e ... 1 .2 1 ,2 1 ,2 1 ,2 1 ,2 1,2 ____ . . . _ ! ----D iffe r e n tia tio n o f a n t h e r s . ________ _______________ ________
1 1
2 1 2
F o r m a tio n o f a n th e r lo b e s
---------1-----A r e h e sp o r ia l c e lls
__________ ________ _________ ________. . . --------------- !____
M o th e r c e ll s ______________
_________ ____ _____________— — — j—
R o u n d in g -u p o f m o th e r c e ll s
-----------:-----R e d u c t io n d iv is io n
........
. _______
T e t r a d s ______________________
;-----M ic r o sp o r e lib e r a t io n ________
•-----A n th e r d e h is c e n c e _______________
'------

2

I

1 1 .2 j
1 1,2 |

2
2

1 22
: 2
il. 2 1 2 '__
1.2 ! 2 ....
1 1 1.2
1 1 1

2

In G roup 2 the flower p rim ordia continue to form as long as
grow th continues in the fall, b u t no differentiation of an th ers occurs

F ig c u t In.— U n fr u itfu l (A . 11) a n d fru itfu l ((.', D ) tw ig s; th e a u x ilia r y b u d s o n b o th t y p e s o f s h o o ts
p r o d u c e s ta m in a te flo w ers th e fo llo w in g s p r in g (0.4H n a tu r a l size)

until the following spring. T h u s the individual flower prim ordia
reach an inactive stage soon afte r form ation and rem ain so for from
four to nine m onths, while ad d itio n al flower prim ordia continue for­
m ation tow ard the actively grow ing term inus. (Fig. 7.) T h u s catk in s
of v a r i e t i e s of G roup 2 tire longer th a n those of G roup 1. T he period
of in activ ity varies w ith the tim e of fo rm atio n — the basal and firstformed ones rem ain inactive longer th a n the new ly form ed term inal
ones; also those formed in buds near the base of the new shoot early
in the season are inactive for a longer tim e th a n those to w ard the
term in u s of the shoot. (Fig. 10.)

June ir., i93o Stam inate Inflorescence and Pollen of Hicoria pecan

1071

fr o m early lull until the anthers arc m ature the following spring
the developm ent of the catkin prim ordia and the catkins of G roup 1
is considerably in advance of th a t of G roup 2. In the fall the differ­
ence is from 2 to 3 weeks; in w inter when grow th is alm ost at a stan d ­
still the m axim um difference of 3 or 4 m onths occurs; while in spring
when grow th is m ost rapid the difference is from 10 to 15 days (figs.
4, 5, 6, and 11), and under some seasonal conditions the shedding of
pollen of the two groups m ay be nearly coincident. (Table 5.)

A

F ig u r e 11.— A , W eak c a tk in s w ith a b o rted flow ers at base; B , v ig o ro u s c a tk in s bra n ch ed a t bn^e;
O, n orm al c a tk in ; D , a b o rted flow ers from w ea k s h o o ts. In d ia n a v a r ie ty . (0.55 natural_sizo)

T he varieties of pecans can be separated into two groups in w inter
on the basis of the internal appearance of the lateral buds. Carefully
cu t and stain ed free-hand sections are sufficient to enable one to m ake
the distinction. P ractical use has been m ade of this fact in determ in­
ing in advance the approxim ate d ate on which pollen of a new or
unknow n variety should shed.
T he p ractical significance of the tim e of pollen shedding of the two
groups will be discussed later. A nthers of varieties of G roup 1 are
differentiated several m onths before pollen shedding and differentia­
tion occurs during th e previous growing season, while differentiation
of anth ers of varieties of G roup 2 occurs about two m onths before
pollen shedding and takes place during the cu rren t growing season,
as is the case w ith pistillate flowers (28 , 21, 12). A closer relation thus
exists in respect to tim e of differentiation betw een stam inate and
pistillate flowers of G roup 2 than between stam inate and pist ill a t c
flowers of G roup 1.

1072

Journal of Agricultural Research

V ol. 40, N o . 12

INFLORESCENCE

A c a tk in prim o rdium consists of th ree regions.
(1) T h e in te rio r region occupies, as seen in lo n g itu d in al section,
alm ost one-half of th e d iam eter of th e prim ordium . I t consists entirely
of large, slightly elongated, p aren ch y m a cells, extending longitudinally
w ith th e axis. T hese rem ain p aren ch y m a cells th ro u g h o u t th e life
of th e ca tk in and are analogous to p ith cells in a young shoot. T he
d iam eter of th e spherical nuclei is ab o u t o n e-th ird th e sm allest di­
am eter of th e cell. T h e nuclei and cytoplasm do n o t stain as heavily
as in th e p aren ch y m a cells of th e p rim o rd ia of individual flowers.
(2) S u rro u n d in g th e in terio r region is a cylinder of sm all, narrow
cells, w ith elongated nuclei w hich m ore th a n half fill th e cells. T he
outline of this region is slightly irreg u lar in b o th cross and longitudinal
sections. In lo n gitudinal section th e cells v a ry g re atly in size and
shape and lie v ery close together. As g row th continues these cells
becom e sclerenchym a cells of th e v ascu lar bundles w hich connect
each flower w ith th e v ascu lar system of th e catkin.
(3) T h e th ird region of th e c a tk in prim ordium consists of individual
flower p rim o rd ia w hich are m ade u p entirely of p aren ch y m a cells from
th e tim e of differentiation u n til S eptem ber. (Fig. 8, A.)
In lo ngitudinal section th e epiderm al cells of th e flower prim ordium
are rounded, uniform in size, b u t som ew hat elongated. T h ey lie
close to one an o th er and form a com plete lay er one cell th ick over the
surface. D irectly b en eath th e epiderm al lay er are closely appressed
3-sided to 6-sided m eristem atic cells w hich v a ry w idely in size. Sec­
tions m ade from m aterial collected A ugust 1 show th a t som e of these
cells are several tim es larger th a n o th ers and are in a s ta te of division.
In th e cen ter of a flower prim ordium are several layers of elongated
cells w ith oblong nucleii. T hese becom e sclerenchym a cells of a v as­
cular system connecting each b ra c t and a n th e r w ith th e vascular
system of th e catkin,
B ra c ts are d ifferentiated ab o u t 10 days before the an th ers. T h e
first ap p earance of th e b ra cts is show n by a tu rn in g of th e term in u s of
th e flower p rim ordia tow ard th e term inus of th e ca tk in prim ordium ,
form ing an angle of ab o u t 45°. As grow th continues th e bend becomes
less a b ru p t an d a p ro tru sio n appears in th e axil. T h is p ro tru sio n
divides im m ediately into four or five sm aller ones, an d each of these
becomes an an th er. (Figs. 8, 7.)
T h e developm ent of b ra cts in spring is v ery rap id . T h re e branches
soon form , th e m iddle one being b ro ad er and longer th a n those on
eith er side. T h e th ree alm ost envelop th e developing anthers.
(Figs. 6, 12.) T h e b racts co n tain chlorophyll, h av e num erous hairs on
th eir surfaces and sm all veins, and presu m ab ly fun ctio n as tru e
leaves.
ANTHER

T h e an th ers of the F ro tsch er v a rie ty on M arch 5 (40 day s before
shedding pollen) were a hom ogeneous m ass of p aren ch y m a cells covered
by an epiderm is. (Fig. 13, B .) V ery early th e a n th e r appeared
4-lobcd in cross section (fig. 14, B ); and th e differentiation of th e
vascular stra n d of th e connective tissue outlin ed th e general plan of
stru ctu re. A lm ost sim ultaneously w ith th e fo rm atio n of lobes, a p late
of h y p o derm al (archesporial) cells becam e d ifferen tiated in each lobe,

June is, 1930 Stam inate Inflorescence and Pollen of Hicoria pecan

1073

fain tly distinguished from th e adjacent cells by their large size,
num erous sides, large nucleii, and less dense staining.
S u b seq u en t divisions up to the m other-cell stage follow one another
very rap id ly . T he archesporial cells divide by periclinal walls, form ­

ing an ou ter layer of p rim ary p arietal (prim ary tap etu m ) cells, and
an in n er lay er of prim ary sporogenous cells; the form er producing the
wall of the em bedded sporangium and the la tte r the sporogenous
tissue. T he p rim ary tap etu m cells successively divide by periclinal
walls u n til six or seven layers are form ed. T he inner layer is known

1074

Journal of A gricultural Research

V ol. 40, N o . 12

as th e endothecium or ta p e tu m , th e o u te r lay er as th e exothecium or
epiderm is, th e th ree or four rem aining layers as “ m iddle lay ers.”
T h e exothecium cells are th in w alled, large and cubical, w ith large
vacuoles and sm all oval nuclei w hich adhere to th e sides of th e cells
to w ard th e cen ter of th e an th er. T he cells of th e m iddle lay er arc
m uch sm aller, som ew hat com pressed, m any-sided, thin-w alled, con­
ta in no vacuoles, h av e nuclei cen trally located, are elongated, and

F ig u r e 13.— E n la r g e m e n ts of F ig u r e 8. A , F ig u r e 8, C X 1,000; B , F ig u r e 8, B X 1,000

stain lightly. T h e thick-w alled, deeply stain in g , 6-sided, closely
pressed, sm all nucleate ta p e tu m cells form a ja c k e t ab o u t th e sporog­
enous cells, one or two cells in thickness.
S im ultaneously w ith th e division of th e p rim ary ta p e tu m cells th e
p rim ary sporogenous cells m u ltip ly w ith o u t definite order to form
m o th er cells. D ivision ap p a ren tly occurs in every direction w ith
occasional form ation of layers b u t no definite m assulae. L o n g itu d i­

June 15,1930

Staminate Inflorescence and Pollen of Hicoria pecan

1075

nally, th e m ass of closely com pressed, m any-sided, large nucleate
m o th er cells extends alm ost th e length of th e anther, and about three
cells wide. (Fig. 15, B .) T h ey stain about as deeply as the m iddle
layers b u t m uch lighter th a n th e surrounding tap etu m cells.
F u rth e r developm ent is accom panied by separation, disorganiza­
tion and d isin tegration of tap etu m cells; and separation, increase in

F

14,— A , C a m e r a lu c id a d r a w in g of cross se c tio n of
a n a n th e r o f A lle y v a r ie ty o n A p r il 5, s h o w in g r o u n d in g -u p s ta g e o f t h e m o th e r c e lls a n d c o n tin u e d d is in te ­
g ra tio n of t h e ta p e tu m cells; X 410: B , cross se c tio n of
a n a n th er of F r o tsc h e r v a r ie ty o n A p ril 5, sh o w in g la ck
o f d iffe r en tia tio n of th e in te r io r in to t y p ic a l t a p e tu m
a n d m o th e r cells; X 410

ig u r e

size, increase in thickness of walls, and rounding-up of the m other
cells. (Figs. 14 and 16.)
T he first evidence of disintegration of th e tap etu m cells occurs
ab o u t 35 days before pollen shedding. (Fig. 15, B .) T he layer of
cells adjacen t to th e m other cells undergoes nuclear division once or
twice, w ithdraw s from the m other cells, shrinks in size, and clusters
around th e m o ther cells in a deeply staining irregular m ass. D isin­
teg ratio n of th e ta p e tu m lay er is increasingly rapid for 15 days, after
w hich d isintegration is alm ost com plete and th e fragm ents form an
109031— 30 ------------- 3

1076

Journal of A gricultural Research

V ol. 40, N o . 12

incom plete lay er around th e m o th e r cells. T h e layers of cells a d ja ­
cent to th e ta p e tu m undergo sim ilar b u t less ra p id disintegration.
T hese cells lose th e ir co n ten ts and th e w alls collect around th e
p eriphery of th e pollen sac. (Fig. 17.) T he epiderm is and th e layer

F i g u r e 1">.— A , C am era lu e id a d r a w in g of cross s e c tio n o f a s to m iu m o f a m a tu r e a n th er; B , lo n g i­
tu d in a l s e c tio n o f a m ic r o sp o r a n g iu m s h o w in g t h e m a tu r e m o th e r c e lls, m , ju s t b e fo re r o u n d in g
up; th e ta p e tu m ce lls, t , s h o w in g th e first s ig n s of d is in te g r a tio n ; th e c e lls b e tw e e n t h e lo c u li. I,
a n d th e e p id e r m is, e

of cells next to it do n o t disintegrate, b u t increase in rad ial diam eter.
T he cells of the m iddle layers continue to d isin te g rate u n til th e pollen
is m atu re and the w asting aw ay of th e wall sep a ratin g tw o loculi on
eith er side of th e a n th er allows th em to fuse in to one, and is a p a r t
of the process of dehiscence.

,iunc la, i93o Stam inate Inflorescence and Pollen of Hicoria pecan

1077

T he m o th er cells do n o t increase in num ber after the tap etu m cells
reach full size (35 to 40 days before pollen shedding). As the tap etu m
cells d isintegrate, th e m other cells become separated and loosely fill

10.—-A, C am era lu c id a d r a w in g of lo n g itu d in a l se c tio n of a n a n th e r of th e A lle y v a r ie ty
on A p ril 1 s h o w in g th e m o th e r c e lls b r e a k in g a p art a n d t h e t a p e tu m c ells r a p id ly d is in te g r a tin g ,
X 110; B , A s h o w n in cross s e ctio n ; X HO; C , e n la rg e m e n t of A ; X 1003. T h e F r o tsc h e r v a r ie ty
r ea ch ed t h is s a m e sta g e on A p ril 15

F igure

the sporangium . R ounding up occurs about 21 days before pollen
and reduction division follows im m ediately.
D ivision of th e m other cells and form ation of tetrad s apparently
require only a few hours and the entire process seems to go to com­
pletion in an an th er at a specific tim e on a single day. (Fig. 18.)
sh ed d in g

1078

Journal of Agricultural Research

vol. 40 , ni. 12

TETRAD

I t is d u rin g th e h e tero ty p ic and hom otypic divisions th a t th e first
abnorm al beh av ior has been observed. T h e appearance of all of the
m o th er cells is norm al, and th e y seem v ery uniform in cell contents,
stain in g reaction, and size and shape. (Figs. 2, 14, and 19.) In the
process of division various types of abnorm alities occur. D ividing
cells were found in th e F ro tsc h e r v a rie ty A pril 26 a t 9 a. m . P ra c ­
tically all steps in th e process of h etero ty p ic and hom o ty p ic divisions
were p resen t in a single an th er. In th e fo rm atio n of new nuclei the
organization of th e ch ro m atin re su lts in nuclei of various sizes and

17.— C am era lu c id a d r a w in g of cro ss s e c tio n o f a n th e r j u s t b efore d e h is c e n c e ( A ) ," a n d la
ta n g e n tia l lo n g itu d in a l s e c tio n of th e s a m e ( B ) ; sto m iu r n at s, S tu a r t v a r ie t y , M a y 13. X 110

F igure

density as d eterm ined by the in te n sity of staining. B ecause of the
m inuteness of the chrom osom es the n u m b er has n o t been definitely
determ ined. In m ost cases the haploid n u m b er w as found to be 12,
in o th ers only 10. In some cases w here th e nucleus was in th e a n a ­
phase stage of th e first division, one or two chrom osom es were lagging
slightly, b u t in some of th e m ore advanced stages th e y h ad com pletely
cau g h t up w ith the o th er chrom osom es.
B o th the successive and sim ultaneous m ethods of division of the
m o th er cells are com m on in pecans, producing b ilatera l an d te tr a ­
h edral arran g em ents, respectively, of the m icrospores. (Figs. 20,
and 21.) In the bilateral arran g em en t th e spindles lie in th e sam e or

Juno is, 1930 Stam inate Inflorescence and Polleyi of Hicoria pecan

1079

in perpendicular planes, and no wall is form ed betw een the successive
divisions. T he two arrangem ents are abou t equally common. No
case has been observed where the four m icrospores were in a row w ithin
the te tra d wall, nor has a failure of four m icrospores to form been
found. Sm all supernum erary m icrospores are often seen which,
according to Shoem aker (19), m ay be the result of sm all nuclei formed
from lagging chromosom es, or, according to C oulter and C ham berlain
(7), from division of one or m ore m em bers of the tetra d . Small
m icrospores are especially num erous in lots of pollen containing a

c

1

F ig u r e 18 — A , C a m era lu c id a d r a w in g of cross s e ctio n of an
a n th er of th e F r o tsc h e r v a r ie ty on A p ril 26 s h o w in g th e
tetr a d s ta g e w ith fra g m e n ts of th e ta p e tu m cells; X 82; B ,
e n la rg e m e n t of A ; X 400. A lle y rea ch ed th is sta g e on A p ril 10

high percentage of defective grains and are alm ost always partially
or to tally void of cell contents. A few oversized grains were found,
and the cell contents of m ost of them appeared norm al. The norm al
n um ber of pores is three, and variance is very rare w ith norm al or
undersized m icrospores; however, oversized m icrospores often have
five or six pores.
A t m a tu rity some of the m icrospores are w ith o u t nuclei and others
w ith o u t either nuclei or cytoplasm . T he lack of protoplasm ic con­
te n ts is the basis of the lactic acid m ethod of determ ining the p ercent­

1080

Journal of A gricultural Research

V ol. 40, N o . 12

age of defective pollen. B y th e use of this m eth o d defective grains
w ere found in all lots exam ined, th e n u m b er ran g in g from 0.3 to 81.7
p er cent.
Flow ers of th e B everage v a rie ty were found in th e te tra d stage on
A pril 24, and co u n ts were m ade as follows: F o u r a n th ers tak en from
th e base of a c a tk in contained 294, 373, 331, and 357 te tra d s, respec­
tiv ely ; and four a n th ers tak en from th e m iddle of th e c a tk in contained
380, 380, 317, an d 488 te tra d s. Since each a n th e r contains four pollen
sacs, and each te tra d contains four m icrospores, th e above figures also

F i g u r e 19.— A , C a m e r a lu c id a d r a w in g o f m a tu r e m o th e r c e lls
th a t a p p e a r n o r m a l; B , m o th e r c e lls w it h a b n o r m a l m ic r o ­
sp o r e s. X 850

rep resen t th e average n u m b er of pollen grains per pollen sac in th e
respective an th ers, th e general average being 365.
L ib eratio n of th e m icrospores (pollen grains) occurs from 15 to 20
days before the pollen is shed. B ecause of th e d isin te g ratio n of th e
ta p e tu m and surrounding cells, th e pollen sac is only p a rtia lly filled
w ith pollen. U pon lib eratio n from th e te tra d wall th e grains w ander
in d ep en d en tly w ithin th e pollen sac and rap id ly enlarge in size, b u t
as th e ca v ity continues to enlarge, owing to th e continued d isin te g ra­
tion of th e su rro unding sterile cells, th e pollen sac rem ains only p a r­
tially filled.

June is, 1930 Staminate Inflorescence and Pollen of Hicoria pecan

1081

DEHISCENCE OF ANTHERS

T h e fusion of th e four pollen sacs into two loculi b y the dissolution
of th e sep aratin g wall occurs only a few days before th e opening of

F

20.— C a m e r a lu c id a d r a w in g s o f s ta g e s o f d iv is io n s of p o lle n m o th e r c ells at 9 'a . m . r
A p r il 26; F r o tsc h e r v a r ie t y . N o t e fo rm a tio n of b o th b ila te r a l a n d tetr a h e d r a l a rra n g em en ts
o f m ic r o sp o r es; a ll h a d r e a ch ed t h e te tr a d sta g e t h e fo llo w in g d a y . X 850

ig u r e

th e a n th e r on either side by m eans of a stom ium , w ith consequent
lib eratio n of pollen grains a t m a tu rity . (Figs. 15 and 17.) The
an th e r wall is two cells thick, w ith fragm ents of one or m ore additional

Journal of Agricultural Research

1082

V ol. 40, N o . 12

layers. T h e opening of th e a n th e r is due to d ry in g of th e ex terio r or
ep iderm al cells an d consequent co n tractio n of th e o u te r in p ro p o rtio n
to th e in n er surface. R eclosing of a n th e rs occurs when m o istu re is

F

i g u r e 2 1 .— C a m e r a lu c id a d r a w in g s o f te t r a d s a n d y o u n g p o lle n
g r a in s: E , F , G , a n d H a p p e a r n o r m a l; K , N , a n d Q c o n t a in m o re
t h a n four m ic r o sp o r es; a t P are sh o w n , p o lle n g ra in s t w o d a y s a fter
l ib e r a tio n from t h e m o th e r c e ll w a ll, s o m e of t h e g r a in s b e in g d e ­
fe c tiv e . X 450

restored. N o opening takes place in an atm o sphere m ore th a n ab o u t
85 p er cent sa tu ra te d . (T ables 2 and 3.)
T a b l e _ 2 .— D ata on dehiscence of rip e anthers when plained in m oist a n d d ry a ir at
different tem peratures
T e m p e r a tu r e

3° C .
22° C
23° C
32° C

H u m id ity

f M o is t
l D r y ._
/M o is t
iD r y ..
/ M o is t
I D r y ..
/M o is t
\D r y _ _

C o n d it io n o f a n th e r s

F a ile d to
D e h is c e d
F a ile d t o
D e h is c e d
F a ile d to
D e h is c e d
F a ile d to
D e h is c e d

d e h is c e .
in 5 d a y s .
d e h is c e .
in 2 d a y s .
d e h is c e .
in 18 h o u r s.
d e h is c e .
in 6 h o u r s .

1083

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M ile s
per hour G ra in s

M ile s
\per hour ; G ra in s Per centi

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1929
Per cent
Apr. 1 8 - .

P o lle n
R e la ­
per
W in d
sq u a r e tive h u ­
v e lo c ity
c e n ti­ m id i t y
m ete r
T em ­
pera ­
tu r e
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R e la ­
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1
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v e lo c ity
c e n ti­ m id it y
tu r e
m ete r
R e la ­
T em ­
tive h u ­ pera­
m id it y
tu r e

IN 1
1
o<N

4.2

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per hour
1
3
10
2
3
4
1
8
4
4

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per
W in d
sq u a r e
v e lo c ity
c e n ti­
m e te r
!i
T em ­
pera­
tu r e

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p era ­
tu r e

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R e la ­
W in d
sq u a r e tive h u ­
v e lo c i t - c e n ti­ m id it y
i m ete r

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D a te

3 p. m. to 6 p. m .
12 m. to 3 p. m .
9 a. m. to 12 m .
j
6 a. m. to 9 a .m .
6. p. m. to 6 a. m .

3.— Summary of data or pollen dissemination

s
V.
O

j Z'L
1

Table

s,O
Ii> M , NO»HCiOOO<f H O OWWW
O O O N iO O
gcOH Or—

1 O’ZS
1

at various times of day in 26 varieties of pecans in the Georgia Experiment Station

orchard

June i5, 1930 Staminate Inflorescence and Pollen of Hicoria pecan

Table

3 .— Summary

of data or pollen dissemination

at various times of day in 26 varieties of pecans in the Georgia Experiment S tation
orchard — Continued

1084
Journal of Agricultural Research
28

d >■

2232S222§3?3S

voi.^o.No. n

:

June is, 1930 Staminate Inflorescence and Pollen of Hicoria pecan

1085

An idea of the m a tu rity of pollen can be had from the stiffness of
the catk in . A catk in th a t would n o t shed pollen w ithin 48 hours is
relatively stiff; one th a t would norm ally shed w ithin 12 hours in warm ,
sunny w eath er is lim ber. W ithin two days after pollen is shed the
catk in becomes dry, very stiff, and falls to the ground.
T he stage of m a tu rity of pollen can best be determ ined by the color
of the an thers. F rom the tim e of em erging from the bud scales u ntil
48 hours before pollen would norm ally shed under suitable conditions,
the an th ers are the sam e color as the bracts and leaves. A fter this
tim e, however, the green color gradually disappears and the anthers
take on m ore and more of the orange-yellow color of the pollen.
W hen fully ripe th e a n th er is pale greenish yellow. If conditions are
suitable, dehiscence will occur im m ediately, b u t if the tem perature is
too low, or the hum id ity above about 85 per cent, the catkin m ay
rem ain for five days or more w ith o u t falling to the ground.
T he ra p id ity of opening of ripe anthers depends som ew hat on tem ­
p eratu re b u t largely on the relative hum idity of the air. On a warm ,
sunny d ay a single a n th er will com pletely shed its contents in an
hour after opening begins. D ue to variations in catkins, twigs,
trees, and varieties under the sam e conditions, a single catkin will
shed pollen for 2 days, a single tree will shed pollen for 5 or 6 days, a
single v ariety will furnish pollen for 10 or 12 days, and a collection of
three or m ore varieties of each group will furnish pollen for ab o u t 3
weeks.
If w ilting was produced very rapidly by the high tem peratures
im m ediately after the catkins were rem oved from the tree, opening
did n o t occur. Likewise, if the relative hum idity was above 82 per
cent the an thers rem ained closed. P a rtly or com pletely open anthers
closed in a few m inutes when subjected to a relative hum idity of
m ore th an 90 per cent. C atkins th a t had fallen from the tree and
become d ry reabsorbed m oisture and the anthers closed in the pres­
ence of high hum idity.
R ecords tak en in the orchard a t 3-hour intervals showed th a t the
tim e of m ost rapid shedding of pollen varied from day to day, d e­
pending on the tem perature and the relative hum idity of the air.
No shedding occurred when the relative hum idity was above 85 per
cent. On some days the peak was reached before 9 a. m. On other
days it was delayed until after 3 p. m., b u t it never occurred between
6 p. m. and 6 a. m. T he tem perature, relative hum idity, and windvelocity d a ta in Table 3 were taken a t the end of the tim e of exposure
of the slides, and in some cases do n o t accurately indicate the condi­
tions th a t prevailed during the period of exposure. The apparatus
for catching pollen (fig. 1, A) rem ained in the sam e place throughout
the pollen-shedding season for three years.
In 1928, in the m idst of the pollen-shedding season, a period of 64
hours elapsed w ith no shedding because of rain. T hree 24-hour
periods occurred during the same season when no pollen was shed.
As a resu lt of low tem peratures and high hum id ity in 1929, not more
th a n 5 days o u t of 21 covered in the pollen-shedding season were
really favorable for pollen dissem ination. T he relative hum idity and
tem p eratu re reached during clear nights w ith a gentle breeze were
not sufficient to cause an th ers already open to close, b u t they did
p rev en t the fu rth e r opening of anthers. A dew or rain which caused

1086

Journal of Agricultural Research

V ol. 40, N o . i2

th e relativ e h u m id ity to rise above 90 p er cent caused all an th e rs to
close and delayed shedding u n til several hours a fte r sunrise on the
following m orning.
Since very high or very low tem p eratu res do n o t occur a t th e tim e
th a t pecans shed th eir pollen, the influence of te m p e ra tu re an d w ind
velocity is chiefly in d irect in re g u latin g the relativ e h u m id ity of the
air. T h o u g h th ere is no opening of a n th ers d u rin g dam p, ra in y
w eather, im m a tu re an th ers continue to reach th e stage of m a tu rity ,
therefore a period of high relativ e h u m id ity followed by a prolonged,
period of low relative h u m id ity is accom panied by th e shedding of a
v ery large q u a n tity of pollen for several hours.
Close observ ation and careful records k e p t for a n u m b er of years
(30) show th a t the length of the receptive period of th e p istillate flow­
ers is as responsive to conditions of te m p e ra tu re an d h u m id ity as th a t
of stam in ate flowers. T h e sam e conditions w hich delay th e shedding
of pollen also prolong the receptive period of th e stigm as. T rees on
w hich the stigm as becam e receptive a t a tim e unfav o rab le for pollen
shedding an d favorable for pollen germ in atio n did n o t have a h eavy
M ay " d ro p .”
T he effect of high h u m id ity is m ainly th a t of re ta rd a tio n . I n ­
stances have been observed in w hich stigm a tic surfaces dried as m uch
in 24 hours u n d er dry, w indy conditions as th ey did in tw o weeks of
dam p, cloudy w eather. D u rin g a prolonged d ro u g h t th e su scep ti­
bility of the stig m atic surfaces to ra p id d rying increases as the recep­
tive stage is approached, and on th e second d ay a fte r becom ing
receptive the roughened surface darkens, shrinks, and dies.
In rain y w eather the receptive stage is reached very g radually,
and afte r ab o u t 10 days th e stigm atic surfaces show sym ptom s of
drying. If cloudy w eath er continues th e stigm as do n o t becom e
com pletely d ry for ab o u t 15 days. T h e n orm al period of re cep tiv ity
of a single flower is ab o u t five days.
O bservations of ab o u t 25 varieties for seven years show th a t during
rain y seasons there are usually enough su n n y days to effect pollina­
tion; and th a t d ry w eather, though op tim u m for pollen dissem ination
often precedes a heavy M ay drop. D a ta in this paper in d icate th a t
the degree of h u m id ity optim um for pollen shedding is not sufficient
to cause germ in ation of pollen; also a low relativ e h u m id ity m arkedly
reduces the v iab ility of the pollen.
T able 4 shows the am o u n t of pollen cau g h t on greased slides a t
various distances from pollen-shedding trees. T h e a p p a ra tu s was
alw ays k e p t on the leew ard side of the trees. T he difference betw een
the am o u n t of pollen caught a t a height of 10, 20, or 30 feet is insignifi­
can t. T h e am o u nt of pollen th a t will be blow n by the w ind depends
on the h u m id ity , tem p eratu re, and velocity of th e circu latin g air.
T he p a th of the pollen from a sm all g ro u p of trees is narrow a t a
given tim e, b u t the horizontal direction of air cu rren ts is likely to
v ary g reatly during the 10 or 12 days of pollen shedding of a single
variety . T h ro u g h o u t the so u th eastern p a rt of the U n ited S ta tes
winds from th e east and south are som ew hat m oist an d are n o t as
conducive to pollen shedding as winds from the west and n o rth w est.

June is, 1930 Staminate Inflorescence and Pollen of Hicoria pecan

1087

T a b l e 4.— A m ou n t of pollen blown by a % to 5 m ile-per-hour w in d fro m a 20-yearvld pecan orchard of M obile, Stu art, and Teche varieties, 1927 and 1928

D is ta n c e from orchard

H e ig h t
fro m
g ro u n d

P o lle n p er D a y after
p o lle n
s q u a r e c en tim e te r
I R e d d in g
b eg a n

Y e a r a n d t im e of d a y

1927
Feet
500 f e e t___
D o ...
D o ...
D o ...
D o ...
D o ...
800 f e e t .. .
D o ...
D o ...
D o ...
D o ...
D o ...
1,000 f e e t .
D o ._ .
D o__.
D o ...
D o ...
D o ..
D o ...
D o ...
D o ...
D o ...
D o ...
D o ...
D o ...
D o ...
D o D o ..
D o ..
D o ..

10

20
30

10
20
30

10
20
30

10
20
30
10

20
30
10

20
30
10

20
30

10
20
30
10
20
30
10

20
30

2 p . m . to 5 p . m . . .
d o _____________
do
................
6 p . m , to 7 a . m ._
d o _____________
d o _____________
8 a. m . to 11 a. m ._
d o _____________
d o . . . ...................
d o ..........................
d o _____________
do
................
11 a. m , t o 2 p . m .
d o ____________
d o ____________
2 p . m . to 5 p . m . .
d o ..........................
do
................
5 p . m . t o 7 a. m . .
d o _______ _____
do
____
7 a, m . to 11 a. m _.
d o ____________
d o ____________
11 a. m . to 2 p . m .
d o ____________
d o ____________
2 p . m . to 5 p . m _ .
d o ____________
d o ____________

G rain s
70 .7
80 .7
92 .6
0 .8
3 .7
4 .5
137.8
162.5
156.5
3 .8
5 .2
5 .6
19.3
2 8 .0
28.3
8 .3
16.6
15.5
13.1
21.4
19.1
11.1
13.2
13.5
64 .9
107.1
134.7
28 .6
4 4 .8
39 .7

F ir st.
D o.
Do
D o.
D o.
D o.
Second.
D o.
D o.
F o u r th .
D o.
D o.
D o.
D o.
D o.
D o,
D o.
D o.
D o.
D o.
D o.
F ifth .
D o.
D o,
D o.
D o.
D o.
D o.
D o.
D o.

10.6
8 .4
10.6
13.3
13.6

F ir st.
Second.
T h ir d .
F o u r th .
F ifth .

1928
3,000 fe e t.
D o ...
D o ...
D o ...
D o ...

2 p . m . to 2 p . m . “ _
d o ______________
d o ______________
d o ______________
d o ______________

» 24 h o u rs.

T a b l e 5.— D ales on which pollen w as shed an d on which p istilla te flowers were
receptive of com m ercial varieties of pecans in leading pecan-growing centers of
southeastern U n ited States
1926

P o lle n s h e d d in g

P is tils r e ce p tiv e

L o c a tio n a n d v a r ie t y o f p eca n
B egan

T if to n , G a.:
A lle y ...................................................................... ..........
B ig Z _________________ ____________________
B r a d l e y .. ______________________ ___________
C u r t is ___________ _________
______________
D e i m a s ............ ................... .................................. ........
F r o tse h e r ....................... ................................ ..............
M o b ile ___________ _________ ____________ _
M o n e y m a k e r ___________
_______________
M o o r e _________ _______ _____________________
N e l s o n . . ....................... ..................................................
P a b s t ............................................. ...................................
P r e s id e n t .......................... ..............................................
S c h l e y ..................... ...................... .........................
S tu a r t....................................... .....................................
S u m m e r s .........................................................................
T e c h e .................................................... ......................
V a n D e m a n ___________ _________ ___________

A p r 27
A p r. 29
A p r. 28
M ay 1
M ay 4
A p r. 26
M ay 1
A p r . 26
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.

28
29
30
26
30
28

Ended

B egan

A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.

30
28
26
28
27
29
28
27
26
27
28
30
28
29
28

A p r . 25

E nded

I SelfG ro u p j p o lliI n a te d

1
2
2
2
2
2
1
2
1
1
1
2
2
2
1
2
2

Y es.
Y es.
Y es.
Y es.
Y es.
Y es.
Y es.
Y es.
Y es.
Y es.
Y es.
Y es.
Y es.
Y es.
Y es.
Y es.
Y es.

1088

Journal of Agricultural Research

V ol. 40, N o . 12

T a b l e 5.— D ates on which pollen w as shed a n d on which p istilla te flow ers w ere
receptive o f com m ercial varieties o f pecan s in leadin g pecan -grow ing centers o f
southeastern U n ite d S tates — Continued
1927

P o lle n s h e d d in g

P i s t i ls r e c e p t iv e
S e lf-

G ro u p

L o c a tio n a n d v a r ie t y of p e c a n
B egan

T if t o n , G a.:
.........
A lle y
B ig Z ...................
B r a d le y .............
C u r tis .................
D e l m a s _______
F r o t s c h e r ____
M o b ile ...............
M o n eym ak er.
M o o r e ________
N e ls o n ________
P a b s t ________
P r e s id e n t ____
S c h le y
.
S u c c e s s ...............
T e c h e ..................
V a n D e m a n ...

E n ded

B egan

E n ded

A p r . 29
M ay 7
A p r . 28
M ay 3
A p r . 29
A p r . 18
M ay 6
A p r . 21
A p r . 26
A p r . 22
A p r . 29
A p r . 26
A p r . 29
— . d o .........
. . . d o ____
. . . d o ____

A p r . 21
A p r . 29
A p r. 21
A p r. 22
A p r . 26
A p r . 12
A p r . 29
A p r . 18
A p r . 21
A p r. 9
A p r. 18
A p r. 21
. - . d o .........
. . . d o .........
. . . d o ____
A p r . 26

p o lli­
n a te d

N o.
N o.
N o.
N o.
Y es.
Y es.
N o.
Y es.
Y es.
N o.
N o.
Y es
N o.
N o.
N o.
Y es.

1928

T if to n , G a.:
A lle y
B ig Z ...................
B r a d le y ..............
M o b ile _______
M on eym ak er.
M o o r e ________
N e l s o n . . - .........
P a b s t _________
P r e s id e n t _____
S c h l e y ________
S u c c e s s _______
T e c h e _________

Tifton, Ga.:
Alley_______
Big,Z .........
Bradley
.
Curtis______
Delmas-.........
Frotscher___
Mobile_____
Moneymaker.
Moore______
Nelson______
Pabst_______
President___
Rome
.....
Schley
.
Stuart.............
Success
.
Summers____
Teche.
.
Van Deman--.
Williams........
Cordele, Ga.:
Frotscher___
Mobile______
Moore______
Nelson______
Schley______
Stuart______
Van Deman__
Albany, Ga.:
Schley
.
Stuart
.
Van-Dcman..

M ay
M ay
M ay
M ay
M ay
M ay
A p r . 28
! M ay 2
I M ay 5
| M ay 2
! M ay 5
L . - d o ____

A p r . 30
A p r . 28
. . - d o ........
A p r . 30
. . . d o ........
A p r . 28
A p r . 21
A p r. 30
. . . d o ____
A p r . 28
. . . d o ____
A p r . 30

A p r . 20

1
2
2
2
2
2
1
2
1
1
1
2
1
2
2
1
1
2
2
2

N o.
N o.
N o.
N o.
Y es.
N o.
N o.
Y es.
N o.
N o.
N o.
Y es.
N o.
Y es.
N o.
N o.
N o.
N o.
Y es.
Y es.

A p r . 19

2
1
1
1
2
2
2

Y es.
N o.
Y es.
N o.
Y es.
Y es.
N o.

A p r . 25
A p r . 26
A p r . 25

2
2
2

Y es.
Y es.
Y es.

A p r . 20
A p r . 21
A p r . 20
A p r . 21

A p r. 18
A p r . 23
A p r. 19
A p r. 21
A p r. 18
A p r . 22
A p r. 21

A p r.
A p r.
A p r.
A p r.
A p r.

22
21
20
25
24

A p r . 20

A p r . 20
A p r . 18

A p r. 22
A p r. 21

A p r . 18
A p r . 19

A p r . 22
A p r . 21

A p r. 21
A p r . 24

A p r . 21

A p r . 23
. . . d o ____
. . . d o ____

Apr? 20
A p r. 22
A p r. 23

A p r . 20
A p r . 20
A p r . 18

A p r . 20
A p r . 29
A p r . 18

A p r . 22
. . . d o ____
. . . d o ____

Y es.
N o.
N o.
Y es.
Y es.
Y es.
N o.
Y es.
Y es.
Y es.
N o.
Y es.

A p r . 22

A p r . 22
. . . d o ____
A p r . 24

A p r . 20
..d o _____
A p r . 23

1
2
2
1
2
1
1
1
2
2
1
2

A p r . 20
A p r . 21
A p r . 20
- . . d o ____

j une is, 1030 Staminate Inflorescence and Pollen of H icoria pecan

1089

T a b l e 5.— D ates on which pollen w as shed an d on which p istilla te flow ers were
receptive o f com m ercial varieties of pecans in leading pecan-grow ing centers of
southeastern U n ited S tates — 'Continued
1929

P o lle n s h e d d in g

P is t ils r e c e p tiv e
G ro u p

L o c a tio n a n d v a r ie t y of p e c a n
B egan

Monticello, Fla.:
Curtis............. .
Frotscher
.
Mahan______
Moore_______
Russell______
Schley
.
Stuart..............
Teche_______
Experiment, Ga.:
Alley
.......
Appomattox..
Beverage.........
Bradley
.
Centennial__
Curtis______
Delmas...........
Indiana...........
Jerome______
Mantura........
Mobile............
Moore.............
Nelson______
Pabst. .........
Randal...........
Robson...........
Rome_______
San Saba____
Schley............
Stuart.............
Success_____
Teche_______
Van Deman...
Thomasville, Ga.:
Frotscher___
Mobile...........
Stuart.............
Schley............
Athens, Ga.:
Alley
.........
Delmas_____
Frotscher........
Jerome______
Mobile..
.
Nelson______
Pabst..............
Success...........
Schley. ___
Stuart______
Teche..............
Van Deman...
Raleigh, N. C.:
Appomattox. .
Bradley.........
Curtis.............
Delmas
.
Frotscher____
Georgia_____
Krakezy.........
Louisiana.......
Manture.........
Mobile______
Moneymaker.
Pabst..............
President........
Russel.............
Schley______
Sovereign____
Stuart______
Success...........
Teche..............
Van Deman...

E nded

A p r.
A p r.
A p r.
A p r . 18

E n ded

A p r . 19

A p r. 25
A p r . 22
A p r, 23

A p r . 21
A p r . 22

A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
A p r.
do.
M ay
A p r.
A p r.
..d o ...d o ..
...d o .
A p r.
A p r.
. .. d o .
A p r.
A p r.
A p r.
...d o .
A p r.
A p r.
M ay

B egan

A p r . 22
A p r . 23
A p r. 21
A p r. 24
M ay 3
A p r. 24
M ay 7
A p r. 25
M a y 12
M ay 7
M a y 12
A p r. 30
A p r. 23
A p r . 24
A p r. 23
A p r. 24
. . . d o ____
A p r. 27
A p r . 24
A p r. 30
A p r, 26
M ay 7
M ay 8
A p r . 26
M ay 7
M ay 8

A p r . 28 M a y 8
A p r . 22 M a y 1
...d o .- i. M ay 6
. . . d o ------ A p r . 26
A p r . 25 M a y 3
A p r. 23 M a y 2
A p r. 21 . . . d o ____
A p r . 30
M ay 8
A p r . 24 M a y 9
A p r . 22 M a y 1
A p r. 22 A p r . 30
. . . d o ____ . . . d o -----A p r. 23
A p r, 24
. . . d o ___
A p r. 22
. . . d o ____
A p r . 25
A p r . 20
A p r. 21

A p r. 22

A p r. 21
A p r . 18

A p r. 22

A p r. 22
...d o .
M ay
A p r.

M ay
M ay
M ay
...d o .
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
doM ay
M ay

M ay 3
M ay 9
M ay 8
M ay 3
M ay 7
M ay 9
A p r. 24
A p r. 28

A p r . 24
. . . d o ___
M ay 3
M a y 15
M ay 6
. . . d o ____
. . . d o -----M ay 3
M ay 9
M a y 13
. . . d o ____
M a y 14
. . . d o ____
M a y 15

M
M
M
M

ay
ay
ay
ay

6
3
1
5

M a y 13
M a y 11
M ay 9
M a y 13

M ay

M a y 13

M ay 2
M ay 3
M ay 2
A p r . 30

M
M
M
M

. . . d o ------ A p r . 29
. . . d o ____
M a y 23 M a y
M a y 19 M a y
M a y 21
M ay 6 M ay
M a y 1 .-.d o M a y 15
M ay 5 M ay
M ay 1 M ay
M a y 16
M a y 15 M a y
M a y 23 M a y
M a y 19 M a y
M a y 23 M a y
M ay 3 M ay
M a y 21
M ay
M a y 18 M a y
M a y 22
M ay
M a y 21

a y 10
a y 12
a y 11
ay 9

M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay
M ay

10
1
19
11
3
23
21
8
18
23
3
23
11
10
17
24
13
24
15
10

S elfp o lli­
n a te d

Y es.
N o.
Y es.
N o.
Y e s.
Y es.
Y es.
Y es.
.N o .
Y es.
Y es.
N o.
N o.
Y es.
Y es.
Y es.
Y es.
Y es.
N o.
Y es.
Y es.
N o.
N o.
Y es.
Y es.
Y es.
Y es.
Y es.
Y es.
N o.
N o,
N o.
N o.
Y es.
Y es.
N o.
Y es.
Y es.
Y es.
N o.
.N o .
Y es.

.Vies.
Y es.
Y es.
Y es.
Y es.
N o.
Y es.
Y es.
Y es.
N o.
Y es.
N o.
Y es.
N o.
N o.
N o.
Y es.
Y es.
Y es.
Y es.
N o.
Y es.
Y es.
Y es.
N o.

Journal of Agricultural Research

1090

V ol. 40, N o . 12

T ab le 5 con tains incom plete d a ta on d ates of beginning an d ending
of pollen shedding and beginning an d ending of re c e p tiv ity of stigm as
of 142 v arieties from eight pecan-producing sections in th ese S tates.
In v arieties of G roup 1 th ere were 31 in stan ces of hom ogam y and
25 in stan ces of com plete dichogam y, all of th e la tte r being p ro tan drous. I n v arieties of G roup 2 th ere w ere 57 in stan ce s of hom ogam y
and 29 in stan ces of dichogam y— 11 in stan ce s of p ro ta n d ry and 18
in stances of pro togyny.

I
F

j

K

22 .— C a m e r a lu c id a d r a w in g s of p o lle n g r a in s in la c tic
a c id m o u n ts ; A , B , C , D , E , H , I , J, a n d K c o n ta in a s m a ll
a m o u n t o f f in e ly g r a n u la r c y to p la s m ; G a n d M are e lo n g a te d
grain s; 11, a gra in w it h s e v e n p ores; F , a n o r m a ] g r a in . X 850

ig u r e

E X A M IN A T IO N

OF

PO LLEN

T h e w riter h as confirm ed S tu c k ey ’s (23) o b serv atio n th a t “ in size,
shape and general ch aracter, the pollen of th e tw o groups of varieties
of pecans differ alm ost none.” H ow ever, th e grains are n o t “ ra th e r
flatten ed , ” as he described them .
D ry pollen grains from a single v a rie ty v a ry slightly in size and
shape, are scu lp tu red, and uniform ly pale yellow. T h e y are spherical
b u t becom e sh ru n k en im m ediately afte r shedding, an d w hen exposed
to very d ry air th e shrinking increases. F resh pollen ta k e n from
an atm osphere 80 p er ce n t s a tu ra te d a t 21° C. an d p laced in an oven
a t 32° lo st 5.5 p er ce n t m oisture; w hen placed in an oven a t 60°
i t lo st 10 p er cen t. D ry grains containing no p ro to p lasm can n o t be
distinguished from those w ith protoplasm . T h o u g h the increased
am o u n t of sh rin k age w hich accom panies th e absence of p ro to p lasm

June i5,1930 Staminate Inflorescence and Pollen of Hicoria pecan

1091

m ay serve as^ a m eans of identifying certain defective grains, m any
abnorm al grains appear norm al w hen dry.
N orm al pollen grains m o u n ted in distilled w ater swell im m ediately
and tu rn d ark. G rains w ith o u t protoplasm fail to swell, and grains
containing p ro to plasm in less th a n the norm al am ount swell so th a t
they are indistinguishable from norm al grains.
W hen m o u n ted in lactic acid, norm al grains become light cream
in color and spherical in outline, and assum e in one m inute an appear­
ance d istin ct from defective grains. T he la tte r either fail to swell
and rem ain opaque, or swell and becom e alm ost tran sp aren t. T he

F

2 3 .— C a m e r a lu c id a d r a w in g s o f p o lle n g ra in s in la c tic a cid
m o u n ts : A , N o r m a l g ra in w it h c o a r se ly g ra n u la r c y to p la s m
(Jero m e); B , C , D , L , a n d M c o n ta in n o c y to p la s m (Jerom e);
F , a gra in o f le s s t h a n n o r m a l s iz e (J ero m e); E , G , H (J ero m e),
I , K (B e v e r a g e ), g ra in s e n la rg e d , a b n o r m a lly sh a p e d . X 800

ig u r e

lack of norm al protoplasm ic co n ten t in certain grains is clearly evident.
Some grains are w ith o u t eith er protoplasm or pores, indicating th a t
abnorm ality began early in th e developm ent; others contain a sm all
am ount of pro to plasm and one or m ore pores; still others have the
norm al n u m b er of pores and swell norm ally, b u t the protoplasm
granules are v ery fine and sufficiently different from norm al grains
to be term ed defective.
A single pollen grain observed in lactic acid am ount is spherical
w ith a roughened surface. W hen the percentage of norm al grains
is high they are extrem ely uniform in size, b u t if th e percentage of

Journal of Agricultural Research

1092

V o l 40, N o . 12

defective grains is high th ere are nu m ero u s large, sm all, an d odd­
sh ap ed grains. (Figs. 22 an d 23.) A n o rm al grain is a b o u t 50 m i­
crons in d iam eter (23) w ith a w all a b o u t 2 m icrons in thickness. T here
is no appreciable difference in th e size of pollen of an y of th e varieties
stu d ied except v aria tio n s due to a larg e am o u n t of defective pollen.
PERCENTAG E

OF

D E F E C T IV E

PO LLEN

T ab le 6 co n tain s d a ta on th e am o u n t of defective pollen found when
169 lo ts w ere exam ined b y th e lactic acid m eth o d . T h e to ta l n u m b er
of grains exam ined w as 169,000.
T able

6 .—

Percentage of defective pollen as fo u n d b y counting 1 ,0 0 0 grains in
lactic acid m ounts, 1928 an d 1929 a
1928

P e c a n v a r ie t y a n d
v ig o r

A ver­
age de­
fe c tiv e
g r a in s

P e r c e n ta g e of d e fe c ­
t iv e g r a in s fo u n d
a t p o s itio n in d i­
c a te d

A p ex

19 .5
3 .0
6 .7
8. 3
35.1
6 .3
5 4
7 .9
6. 4

M id d le

B ase

3. 7

2 .5

2 .9

10. 2
33. 5
8. 6
4. 4
9. 2
6. 0

8 .9
34. 5
6. 7
7 .6
3 .1
7. 3

6 .3
3 7 .1
4 1
4. 1
6. 3
6 .0

Jerom e:
N o n v ig o r o u s

N e ls o n

____________

2 7 .2
3 5 .2
7 1 .2
23 .8
20. 2
20 .2

P e c a n v a r ie t y a n d
v ig o r

A ver­
ag e de'
f e c tiv e
g ra in s

3 2 .4
3 1 .6

3 7 .1
3 3 .5

4 2 .2
4 0 .5

10. 6

4 4 .8

16.3

P e r c e n ta g e of d e fec ­
t iv e g r a in s fo u n d
a t p o s itio n in d i­
c a te d

A p ex

P a b s t:
V ig o r o u s _____
N o n v ig o u r o u s
R a n d a l___________
R o b s o n ___________
R om e
............
S a n Saba:
V ig o r o u s ............
N o n v ig o r o u s_ _
S c h le y ..........................
S t u a r t ..........................
T e c h e _____________
U nknow n
.
V a n D e m a n ............
W auchenah
-_

M id d le

B ase

4 .5
4 .4
5 .9
7 .1
2 9 .6

6 .7

1 0 .3
1 3 .4
1 4 .3
4 6 .6
7 .5
13.1
2 9 .2
5 .8

14 7

5 .4

1 1 .3

12.8

16.0
2 7 .6
5 .1
9 .4
4 4 .5
6 3

14 .0
20 . 6
9 .4
1 7 .6
3 7 ,5
5 .3

81. 7

8.0
12.2
35. 6
5. 7

4 .0

1929

A verP e c a n v a r ie t y

L o c a tio n

V ig o r

P e r c e n ta g e o f d e fe c ­
t iv e g r a in s fo u n d a t
p o s itio n in d ic a t e d

fe c t iv e
g r a in s
A p ex

A lley.....................
E x p e r im e n t , G a .
Appomattox______
- - . - d o ...... ............... .
Beverage
.........
do
.............. .
Bradley______ ____
d o ___________
Centennial________
do
_____
Curtis
..............
d o ___________
Delmas______ ____
d o ___________
Ga. Giant________
T if to n , G a ______
Indiana__________
E x p e r im e n t , G a .
Jerome
______
do
.........
Mahan
______
M o n t ic e llo , F l a - .
Mantura--------------------- Experiment, Ga
McAlister_______
do....... .........
Mobile_________
...d o ________
Do
----------Oordele, Ga.............
D o.
.............. . Milner, Ga____
D o.............................. Barnsville, G a..
Do_______________ . . ...d o .................
Do..............................j____ do________
D o----------do..... ...........
Do.......................
do________
Do
.....................
do________
Do_______________I_____do________

M e d iu m
.
d o ________
d o ________
d o ________
d o ________
d o ________
V ig o r o u s _____
d o ________
M e d iu m _____
d o ________
V ig o r o u s ..........
M e d iu m ..........
d o . _ ..........
d o ..
.
d o _______
V ig o r o u s
.
d o ________
d o ________
d o _______
M e d iu m _____
d o ________
N o t v ig o r o u s .
d o . . ..........

M id d le B a s e

10.2
.3
.9
6 .9
3 1 .7
4 .6
7 .0
1 0 .4
3 .3
3 .3

1 .4
7 .7

4 .3

1 .4
4 .4

0
8 .5

2 .3

4 .4

12.0
20.0

8.2
1. 1
8 .4
1 .7
3 .7

.8

1 .4

2. 6

8.0
5 .4
3 .6
3 .0
2 .3

_ a P o lle n from v a r io u s p e c a n v a r ie t ie s w h e n e x a m in e d in 1 9 2 9 ,1 3 y e a r s a fte r c o lle c tio n , s h o w e d t h e f o llo w m g p e r c e n ta g e s of d e f e c t iv e g r a in s: F r o tsc h e r , 4.5; M o n e y m a k e r , 6.2; P a n A m e r ic a n , 9 8: P i e s i d e n t , 4 1*
T e c h e , 30.6; V a n D e m a n , 3.
'

1093

June 15,1930 Staminate Inflorescence and Pollen of Hicoria pecan

T a b l e 6.— Percentage o f defective pollen a s fo u n d by counting 1,000 g rain s in
lactic acid m ounts, 1928 and 1929 —-Continued
1929

P e c a n v a r ie ty

L o c a tio n

V ig o r

M o o r e ___________________
..........d o ............................................
B a r n s v ille . G a ____________ _____d o _______ _______
E x p e r im e n t, G a ___________
...d o
. .
R o b s o n . _______________
......... d o .............................
S an S a b a .................... ............
D o ......................................
P a b s t ........................................

D o ......................................
D o __________________
D o . . ..................................
S u m m er s .............................
S tu a r t........................................
S u c c e ss.....................................
T eche . .
.................. . . .
V a n D e m a n ..........................
D o ...................................... ____ d o ___________
D o ......................................
D o . . . _______________
D o __________________
W a u c h e n a h ...........................
W illia m s ....... ..........................

P e r c en ta g e of d efec­
A v e r ­ t iv e grain s fo u n d at
p o s itio n in d ic a te d
age d e­
fec tiv e
g ra in s
A p ex M id d le B a s e

6 .3
5. G
12 .3
1 .0
6 .5
2 .7
5 .2
5 .9
6 .0
37 .5
6 .0
16.4
7 .2
3 .7
1.2
41.0
32.1
4 0 .0
9 .6
26 .0
11.2
10.4

6 .7
6 .8

9 .8
5 .4

2 .5
4 .6

1.1

.9

.9

3 .7
5. G

3 .2
7 .8
5.7

2 .2
2 .9
6 .5

36 .6

4 6 .0

4 1 .5

F e r tiliz e r

S t u a r t ........... ........ ...................
D o __________________
D o ______________ _
D o ......................................
D o ................ .....................

Do............................

E x p e r im e n t, G a ..................
____ d o ____ __ . . . ________
____ d o _____ _____
____
..........d o ........................................... H ig h N ............
..........d o ............................................ H ig h K _______
____ d o .
__________________

5 .4
3 .0
5. G
S. 6
7 .2
6 .5

In 1928 pollen was m uch m ore plentiful in the orchards th a n in 1929,
and th e percentage of defective grains was ab o u t twice as high. T h e
differences betw een th e percentages of defective pollen shed from th e
apex, m iddle, and base of th e sam e catkins is negligible. T he C enten­
nial and M a n tu ra were the only varieties th a t produced pollen m ore
th a n 19 p er cent of w hich was defective in 1928 and 1929, and the
P a b st was th e only v ariety th a t produced pollen less th a n 5 per cent
of which was defective in b o th years. T he v ariatio n in percentages of
defective pollen of the M obile variety, tak en from four localities and
from trees of unequal vigor in 1929, is very sm all; also the v ariatio n in
percentages of defective pollen tak en from S tu a rt trees w hich received
different lands of fertilizers is insignificant. O n th e o th er han d ,
Schley pollen from nonvigorous trees a t Griffin h a d ab o u t six tim es as
high a percentage of defective pollen as th a t g ath ered a t E xperim ent,
Bacon ton, or T ifton, and V an D em an pollen from vigorous trees a t
Cordele h ad ab o u t one-third as high a percentage of defective pollen
as th a t from trees of m edium vigor a t B aconton an d ab o u t one-fourth
as high as th a t from vigorous trees a t E x perim ent or T ifton.
T able 7 shows th e m agnitude of v aria tio n of defective grains in
successive lots of 100, th a t is, th e percentage of defective grains in
successive lots. ^ T h e table includes 6 varieties an d 12 lots of 1,000
grains each w hich were shown in T able 6 . In general, it m ay be
said th a t in counting 1,000 grains in lots of 100 grains each, the

Journal of Agricultural Research

1094

V ol. 40, N o . 12

low est percen tag e of defective grains is a b o u t h alf t h a t of th e highest
p ercentage.
T

7 .— M agn itu de of the variation (per cent ) o f defective g rain s as counted in

able

successive lots of 100
P e r c e n ta g e o f d e fe c tiv e
g r a in s in p o lle n from —

P e r c e n ta g e of d e f e c t iv e g r a in s a t p o s itio n m e n tio n e d in p o lle n fro m —

C e n te n n ia l

S c h le y

Jerom e

A lle y
A p ex

M id d le

B ase

A p ex

M id d le

B a se

A p ex

M id d le

M antu r a

C u rtis

B ase

34
30
35
35
32
33
43
34
45
19

32
34
30
34
38
40
29
36
34
38

30
32
33
44
41
44
42
34
33
38

33
19
36
24
40
30
36
31
40
35

33
35
47
37
33
35
46
34
39
30

44
38
42
40
45
43
47
54
39
30

11
13
9
15
10
16
10
15
17
12

20
14
16
15
22
17
13
17
14
12

13
21
15
12
9
8
16
13
18
14

30
16
16
13
17
19
25
21
17
21

57
72
80
57
74
74
68
77
28
81

54
51
52
53
54
77
60
56
56
48

33 .5

3 4 .5

37.1

3 2 .4

37. 1

4 2 .2

12.8

16

14

19. 5

7 1 .2

56 .1

T h e d a ta recorded in T ab le 8 w ere o b tain ed w hen th e ru b b er-rin g
cells w ere used, as previously described.
T able

8 .—

P ollen germ in ation under va ryin g conditions
S E R I E S 1 <■

Sugar u sed

M a lt o s e ..
D o ...
D o ...
D o ...
S u cro se. _
D o ...
D o ...
D o ...
L a e to s e ..
D o ...
D o ...
D o ...
G lu c o s e ..
D o ...
D o ...
D o ...
F r u c to se .
D o ...
D o ...
D o ...
G a la c to se
D o ...
D o ...
D o ...

S tr e n g th

P e r cent
20
15
10
5
20
15
10
5
20
15
10
5
20
15
10
5
20
15
10
5
20
15
10
5

G e r m i­
n a tio n

0 .5
.5
1 .0
1 .0
2 5 .0
3 0 .0
50. 0
4 0 .0
5 0 .0
4 0 .0
3 0 .0
3 0 .0
1 5 .0
1 0 .0
5 .0
2 .0
0
.5
1 .0
1 .0
2 0 .0
15 .0
10.0
5 .0

T u b e le n g th

S h o r t.
------- d o
- - .d o
.d o
L o n g ..
------- do
- ..d o
------- do
- .- ..d o
.d o
------- do
------- d o
Short
------- d o
..........d o
----- d o
------- do
- - - .d o
- ..d o
- - - .d o
- ...d o
----- d o
.d o .
.d o

Grains
b u r s tin g

F ew .
D o.
D o.
D o.
N on e.
D o.
D o.
D o.
D o.
D o.
D o.
D o.
F ew .
D o.
D o.
D o.
D o.
D o.
D o.
D o.
D o.
M any.
D o.
D o.

<* U s in g 2 p er c e n t a gar, p o lle n s to r e d in la b o r a to r y for 24 h o u r s, g e r m in a t io n a t 25° C ., 4 d r o p s of w a te r in
b o t to m of cell.

109 5

June 15,1930 Staminate Inflorescence and Pollen of H icoria pecan
T a b le

8. — P ollen germ in ation under varyin g con dition s — C o n tin u e d
S E R IE S 2 *

A m ount
u sed

G er m i­
n a tio n

P e r cent
1 .0
.5
.I
1 .0
.5
D o ___________________________
.1
Do
..
.......................
1 .0
.5
. 1
D o ........................................................
1 .0
S o d iu m h y d r o x id e ....... ........................
.5
___
_____________
Do
. 1
Do
. ______________ ____
.0 3
D o ............ - _______ _____________
.025
D o _______ ____________________
C h e c k ______
_______________

P e r cent
75
80
85
0
0
0
20
50
75
0
0
0
20
30
75

R eagen t added

D o .................................. .....................
D o _________ __________________

T u b e le n g th

L o n g ..
do.
do.

G ra in s
b u r stin g

R em arks

P e r cent
10
10

10

0
0
0

L o n g ..
do.
do.

10
15

20

0
0
0

L o n g ..
do.
do

S ta in e d b r o w n .
D o.
D o.

20

20
10

S E R IE S 3 ■

S torage c o n d itio n s

Sto ra g e
p erio d

H o u rs
F r e s h .................... .............................. .................
M o is t c h a m b e r . . ............
.............. ..
25° C ., d r y ....... ................. ..............................
L a b o r a to r y ____
_________
. ..
_________ . .
M o is t c h a m b e r _____
25° C ,, d r y . ............................. .........................
L a b o r a to r y ...............................
............
M o is t c h a m b e r ________ .
. ..............
O n i c e .. ...........................................................
O n ic e _____ _________ . . ........... ....
M o is t c h a m b e r .. __________ ______ ____
O n ic e ................. ..................................................
I n m a il, m o is t ___________
____
I n m a il, s e m i m o i s t ..
________
I n m a il, d r y _____ __'
.........................
In m a il, m o i s t .. . ___________ _________
I n m a il, s e m i m o i s t . . .......... . . _ ____
I n m a il, d r v ___ __
_ ________

48
48
48
48
48
72
72
72
72
16
96
90
1.0
1 .0
1 .0
144
144
48
43
48
192
192
192

G erm i­
n a tio n

T u b e le n g th

P e r cent
7 0 .0
25. 0
0
3 0 .0
20 .0
40. 0
15. 0 ___ d o . . . .
10. 0
0
30. 0
.2
10 .0
10 0
0
5. 0
10.0 ......... d o .......................
0
2 .0
2 5 .0
1 0 .0 ......... d o ___
5 0
5 0
2. 0
0

G ra in s
b u r stin g

N on e.
D o.
D o.
D o.
D o.
E ew .
M any,
D o.
N on e.
M any.
F ew .
D o.
M any.
N on e.
D o.
M any.
N on e.
M any.
D o.
D o.
D o.
D o.
D o.
Few .

&U s in g 10 per c e n t su c r o se , 1 ^ p er c e n t agar, S u c c e ss p o lle n sto r e d in la b o r a to r y for 21 h o u r s, g e r m in a ­
tio n a t 22° C ., cell h a lf fille d w ith w a te r .
e U s in g 20 per c e n t su c r o se , 2 p e r c e n t agar, g e r m in a tio n a t 25° C „ 4 d ro p s o f w a te r in c e ll.

Journal oj Agricultural Research

1096

V ol. 40, N o . 12

T a b l e 8 .— P ollen germ in ation under va ryin g co n d itio n s— C o n tin u e d
S E R I E S 4 **

P e r c e n ta g e g e r m in a tio n u n d e r s to r a g e c o n d itio n s in d ic a t e d
P e r io d
of
sto r a g e

P e c a n v a r ie t y

D ry

S c h le y ....................... . _______ . . .
S t u a r t ........................................... ...........
S c h le y .................................... . . . . .
S t u a r t .............. .................
................
S c h le y ______________ __________
S t u a r t . . ........................... ................. ..

. . _________
N e l s o n ................... ..
R o b s o n .................................... .. . . .
C e n t e n n ia l_______________ . . . .
. .. ..
A l l e y __________ _____ _

H ou rs
24
24
24
48
48
48
72
72
72
96
96
96
120
120
120
120
120
120
120
120

23° c .

32° c .

M o is t

D ry

I n o rch a rd

22= c .

M o is t D r y

0
0
0
0
0
0

0
0
0
0
0
0

0
0
0
0
0
0

65
80
50
50
65
30
0
0
0

0
0
0
0
0
0

0
0
0
0
0

0
0
0
0
0

0
0
0
0
0

0
0
0
0
0

0
0
0
0
0

M o is t D r y

65
80
50
55
70
40
20
25
10
0
0
0
—

-

M o is t D r y

30
45
25
0
0
0

64
so
45
60
75
45
30
45
20
15
25
10
0
0
0
0
0
0
0
0

_

0
0
0
0
0

5° c .

0
0
0
0
0

M o is t

50
65
45
25
35
20
0
0
0

65
80
60
75
45
55
65
40
30
40
25
3
5
0
0
3
2
0
1

0
0
0
0
0

SERIES a*
1
P e r c e n ta g e g e r m in a ­
t io n of—

P e r c e n ta g e g e r m in a ­
t io n of—

G e r m in a tin g te m p e r a ­
tu r e

G e r m in a tin g te m p e r a ­
tu r e
S c h le y

3° C ............................................
22° C ______________________

0
60

S tu a r t

0
75

V an
D em an

0
50

S c h le y

S tu a r t

V an
D em an

65
0

80
0

50
0

1
23° C
32° C

d U s in g 20 per c e n t s u c r o se , \ } i p er c e n t agar, g e r m in a tio n a t 23° C ., c e lls h a lf fille d w it h w a te r (p e rc e n ta g e
g e r m in a tio n ).
* U s in g 10 p er c e n t s u c r o se , 1 \ i p er c e n t agar, c e ll h a lf fille d w it h w a te r , fresh p o lle n .

M ed ia co n tain ing 10 p er ce n t sucrose, \ }{ p er ce n t ag ar, plus e ith e r
one of th e following form ed a p re cip itate, failed to solidify a t 20° C .,
and w as n o t u sed: U n ited S ta tes P harm acopoeia citric acid, 1, 0 .5 ,
an d 0.1 p er c e n t; 91 p er cen t lactic acid, 0.5 an d 0.1 p e r ce n t; U n ited
S ta tes P h arm aco poeia tan n ic acid, 1 p er cent.
U n d e r su itab le conditions pollen began to g erm in ate in 1% hours
an d com pleted g erm ination in 12 hours, b u t 14 to 18 h o u rs were
req u ired for pollen tu b es to reach full len g th before b u rstin g . If
allowed to rem ain longer th a n ab o u t 18 h o u rs th e tu b es b u rs t and
em p tied th e ir c o n te n ts into th e surrounding m edium . (Fig. 24.)
B u rstin g of pollen tu b es is d istin c t from “ pseudo g e rm in a tio n ” or
b u rstin g of u n g erm in ated grains as described b y A ndronescu (1) and
as used in T able 8 . If th e conditions rem ain favorable for g ro w th
all of th e pollen tu b es will b u rs t in ab o u t 30 hours.
N o tu b es in artificial m edia have been found to b ra n ch , as occurs
in th e tu b e g ro w th in th e pistils (31); n o r h as a n y of th e g erm in atio n
p ercentages equaled th e percentage of n orm al pollen as show n by
co u n ts in lactic acid.

Ju n e

is, 1930 Staminate Inflorescence and Pollen of Hicoria pecan

Pollen failed to germ inate in pure w ater, or in any concentration of
agar which did n o t solidify a t 25° C. S atisfactory results were
obtained w ith l){ or 2 per cent agar w hen sugar was added. N o
germ ination was obtained when no w ater was placed in th e cell to
provide m oisture for th e pollen. F rom four to eight drops of w a te r
were found best for th is; less th a n this am ount did n o t keep th e pollen
sufficiently m oist for germ ination, and m uch m ore th a n this caused
excessive b ursting of grains.
D a ta in T able 8 show th a t of the six sugars used in the m edia for
germ inating pollen, lactose and sucrose gave highest percentage

F i g u r e 24.— C a m era lu e id a d r a w in g o f sta g e s in th e g e r m in a tio n of

p o lle n grain s on sugar-agar m e d iu m : A , N o r m a l g e r m in a tio n ; B ,
fo rm a tio n of t w o tu b e s from a sin g le p o lle n grain; B a n d E , s w e ll­
in g a t en d o f tu b e w h ic h m a y la ter burst; C , t w o n u c le i in th e
p o lle n tu b e; D , a n o r m a l tu b e ; F , se ctio n of a p o lle n gra in 10 d a y s
before sh e d d in g . X 750

germ ination and least bursting of the grains; galactose and glucose
produced fair germ ination; and fructose and m altose c a u s e d ’ an
extrem ely low percentage germ ination and a high percentage of
bursting.
O ne-tenth of 1 or one-half of 1 per cent asparagine w hen added to
the m edium produced a slight increase in percentage of g erm ination;
1 per cent n eith er increased nor decreased the percentage of germ ina­
tion. M ore th an 0.1 per cent of peptone caused a decrease in p e r­
centage of germ ination. T annic acid prevented germ ination w hen 1,
0.5, or 0.1 per cent was added to th e m edium . Sodium hydroxide
decreased germ ination when as low as 0.025 per cent was added to th e
medium , and m ore th a n 0.1 per cent prev en ted germ ination.

Journal of Agricultural Research

1098

V o l. 40, N o . 12

P ollen w as stored u n d er te n te m p e ra tu re and h u m id ity conditions.
T h a t stored u n d er b o th m oist and d ry atm ospheric conditions a t 32° C.
lost its v ita lity in 24 hours. T h a t sto red a t e ith e r 23° o r 22° in a
d ry atm o sp h ere did n o t g erm in ate afte r 24 hours, b u t o th e r lots
g erm in ated afte r being stored for 48 and 72 hours, respectively, u n d e r
m oist conditions. T h a t stored d ry a t 5° g erm in a te d a fte r 48 hours,
an d th a t sto red m oist germ in ated a fte r 96 hours. N o te m p e ra tu re
an d h u m id ity condition w as found u n d e r w hich pollen could be stored
for longer th a n 96 h ours w ith c e rta in ty of g erm ination. T h e op tim u m
te m p e ra tu re for g erm ination was found to be ab o u t 23° C.
R E L A T IO N

O P SIZ E O F C R O P P R O D U C E D I N O N E Y E A R T O N U M B E R
P R O D U C E D T H E F O L L O W IN G Y E A R

OF FLOW ERS

In T ab le 9 is show n th e relatio n betw een th e size of crop of n u ts of
one y e a r and th e size of crop of stam in ate an d p istilla te flowers of th e
n ex t y ear. In o rder th a t th e d a ta from trees of different v arieties and
ages m ig h t be com parable, each tree w as ra te d an d placed in one of
six groups. T h e su m m ary of all varieties shows t h a t a large or v ery
large crop of n u ts is followed by a som ew hat reduced crop of b o th
sta m in a te and p istillate flowers th e following season; an d no crop or a
fair, poor, or v ery poor crop of n u ts is followed by a large crop of b oth
sta m in a te an d p istillate flowers.

/

T a b l e 9 . — R elation between the size of crop of nuts o f one year a n d the produ ction o'

catkin s and p istilla te flow ers the fo llo w in g yea r
[ A = v e r y large crop; B = la rg e crop; C = fair crop; D = po o r crop; E = v e r y p o o r crop: F = n o crop]
R a t in g o f 1929 cro p
of—
P e c a n v a r ie t y

A g e of
tree

1928 cro p o f n u t s

1928 cro p
r a tin g

Y e a rs
A l l e y ______________ ____ _ _
___
D o ________ _____________________
D o .......... ..................................... .............
D o ............ .................................................
D o .......... ...................................................
A p p o m a t t o x _ __ _____________ . . .
A t la n ta
..
_____________________
B everage . . .
. __
_________
B r a d le y _____
. ..
.....................
C e n t e n n ia l.
. ..
.. . _ _
C u r t is ___ _______ _______________
D e l m a s ..................
_ ...
. . . __
D o ________ _____________________
D o _____ ______ __________________
D o ______________________________
D o _____ ______ _________ _____ _
D o _________ ______ ____________
D o ___________________ __________
F r o tsc h e r . ________ _____ _________
D o ______________________________
D o ______________________________
D o ............................ .................................
D o ______________________________
D o ______________________________
D o ______________________________
D o ______________________________
D o ______________________________
D o ______________________________
D o ______________________________
D o ________ _____ ________________
D o ________ _____________________
D o ______________________________
D o . . _________ __________________
D o _______________
_________
J e r o m e ___________ _______ ________
M a n tu r a ___ __ ____________ _ . .

D
D
D
C
C
B
A
D
B

7
7
18
20

18

20
20
20
20
18
12
18
18
18
20
20
20
20
20
10

E

B
D
D
D
D
E
E
E
A
A
A
A
B
B
B
B
B
B
B
B
B
B
B

10

20
20
20
20
20
20
20
20
20
20
20
12
12
20
20

34 p o u n d s ____ ______

E
E
c
C

C a t k in s

P is tilla t e
flo w er s

c
c
c

B
B
B
D
D
B
F
A
A

A
A
F
F
A

c
F

B

A
B
B
B
A
A
A
F
F
E
E

c
c
C
c
c
c
c
c
c
c
c
A

c

E
A
A
A
A
A
A

F
F
B
B
B
B
B
B
B
B
B
B
B
B
B

F

j une is, 1930 Staminate Inflorescence and Pollen of Hicoria pecan
T a b l e 9.

1099

R elation between the size of crop of nuts of one year an d the production of
catkins an d p istilla te flow ers the follow in g year— C o n tin u e d
R a tin g of 1929 crop
of—

P e c a n v a r ie t y

A g e of
tree

1928 crop
r a tin g

1928 cro p of n u ts

C a tk in s

D o .............................................................
D o _______ ______ ________ _______
D o ______________________________
D o ______________________________
D o .............................................................
D o .............................................................
D o .............................................................
D o ______________________________
D o ______________________________
D o ______________________________
D o __________ ______________ _____
D o .............................................................
D o _______________ ______________
D o ______________________________
D o ______________________________
D o .................................... ........................
D o .............................................................
D o ............................................... .............
D o __________ __________ ________
D o ______________________________
D o ............................................................
D o ____
____________
D o .............................................................
D o .................................... ........ ...............
D o ____
____________
Do
.
__________
D o .............................................................
D o _______
____________
Do ...
.........................
D o.
.......................
Do
D o.
.
Do
.......................
D o .................................... ............. ...........
D o ........
.........................
Do
___
Do

Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do
D o . . ........................................................
0 N u t s p o o r ly fille d .

Y ears
18
18
18
18
18
18
18
18
18
18
18
18
25
22
11
11
11
11
11
11
11
20
12
12
20
18
19
19
19
19
19
19
19
19
19
19
19
19
16
16
16
20
20
20
12
20
18
12
18
18
18
8
9
18
18
18
18
18
22
22
22
22
22
16
18
20
18
18
18
18
18
18
18
16

4,704 n u t s °

33 p o u n d s .. ____ ____________
43 p o u n d s ........................................

P
F
F
F
F
F
F
F
A
A
D
A
D
A
A
A
A
A
A

A
C
b

1,504 n u ts

___

1,779 n u ts *.....................................
91 p o u n d s ___________
- ...

40 p o u n d s .. ............
25 p o u n d s .. . . . .

... ... -

22 p o u n d s _____ ___________

.

615 n u t s . .................... . . . .
689 n u t s . . . . ------------2,161 n u t s . .................. ........
1,961 n u t s . . ------- ------------------999 n u t s .................... ------2,136 n u t s ____________________
1,273 n u t s ____________________
992 r u t s ______________________
1,533 n u t s ------------ -----------------852 n u t s . ---------- ---------------------

E
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
C
0

c
c

A
A
A
A
B
B
A
A
A
A
A
D
D
D
D
E
B
C
E
C

c

D
C

c

D
C

c

E
A
A
A
A
A
A
A
A
A
A
A
F
B
F

F

F
F
F
F
F
F
A
A
B
B
E
E
E
E
E
E
E
E
E
E
E
E
A
A
A
B
F
B
B
B
B
E
C
C

c
c
c

D

C
B
B
B
B
B
B

c
c

D
D
A
B
B
B
B
B
B
B

c

P is tilla te
flow ers

A
A
A
A
A
A
D

c

A
F
B
F
F
F
F
F
F
F
F
A
A
F
F
B
F
F
F
F
F
F
F
F
F
F
B
B

c

B
F
F
D
B
B
B
E
A
A
A
C
E
A
A
A
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B

Journal of Agricultural Research

1100

V o l. 40, N o . 12

T a b l e 9 . — R elation between the size o f crop o f n u ts o f one year a n d the produ ction

o f catkin s a n d p istilla te flow ers the fo llo w in g y ea r — C ontinued
R a t in g o f 1929 cro p

of—

P e c a n v a r ie t y

A ge of
tr e e

1928 cro p o f n u t s

1928 c r o p
r a tin g
C a t k in s

Yea
S tu a rt
.
D o _____
D o ..........
D o ..........
D o ..........
D o ...........
D o ...........
D o ...........
D o _____
D o ...........
D o _____
D o ...........
D o ...........
D o _____
D o ..........
D o ...........
D o ...........
D o ...........
D o ...........
D o ...........
D o _____
D o ..........
D o ...........
D o ...........
D o ..........
D o ...........
D o ...........
D o ...........
D o ...........
D o _____
D o ...........
D o _____
D o ...........
D o _____
D o ..........
D o ...........
D o ..........
D o ..........
S u c c e s s _____
T e c h e .............
D o ...........
D o _____
D o _____
D o _____
D o _____
D o ...........
D o ...........
D o ...........
D o ...........
D o ...........
D o ...........
D o _____
D o ...........
D o ...........
D o _____
D o _____
V an D em an
D o _____
D o _____
D o _____
D o ...........
D o _____
D o ...........
D o ..........
W ils o n _____
D o ..........

717 n u t s . .
lo 4 n u t s ..
763 n u t s . .
607 n u t s . .
625 n u t s . .
663 n u t s . .
3 p o u n d s ..
2 p ou n d s.
7 p ou n d s.
1 p o u n d ...
4 p o u n d s .,
17 p o u n d s
l p o u n d ..
4 p o u n d s .,
3 p o u n d s .,
7 p ou n d s.
16 p o u n d s
3 p ou n d s.
13 p o u n d s
9 p ou n d s.
12 p o u n d s
17 p o u n d s.
17 p o u n d s
6 p o u n d s ..
9 p o u n d s .,
1 p o u n d ..
16 p o u n d s
9 p ou n d s.
9 p ou n d s.
6 p o u n d s .,
6 p o u n d s .,
17 p o u n d s
6 p o u n d s .,
8 p o u n d s .,
U pounds
16 p o u n d s
8 p ou n d s.
2 p o u n d s .,
4 p o u n d s .,
55 p o u n d s
81 p o u n d s
61 p o u n d s
71 p o u n d s
258 n u t s ..
1,083 n u ts .
1,167 n u ts .
434 n u t s .. .
24 p o u n d s
21 p o u n d s
18 p o u n d s
8 p o u n d s ..
18 p o u n d s
15 p o u n d s
7 p ou n d s.
24 p o u n d s
20 p o u n d s
19 p o u n d s

P i s t i ll a t e
flo w er s

June is, 1930 Staminate Inflorescence and Pollen of Hicoria pecan

1101

T a b l e 9 . — R elation between the size of crop o f n u ts of one year an d the production

o f catkins a n d p istilla te flow ers the follow in g year — Continued
R a t in g o f 1927
cro p of—
P e c a n v a r ie t y

M o b ile .....................
D o .....................
D o .....................
D o ............ ..
D o __________
D o _____ _____
D o .....................
D o .....................
D o .............. . . .
D o __________
S tu a r t___________
D o ......................
D o .....................
D o ...................
D o __________
D o __________
D o .....................
D o . ...................
D o ............ ..
D o _________
D o .................

A g e of
tre e

1926
cro p
r a tin g

Y ears
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9
9

A
A
A
A
A
A
A
A
A
A
C
C

c
c
c
c
c
c
c
c
c

R atin R of 1927
cro p o f—
A g e of
tre e

P e c a n v a r ie t y
C a tk in s

P is til­
la te
flo w er s

F
F
F
F
F
F
F
F
F
F
A
A
A
A
A
A
A
A
A
A
A

F
F
F
F
F
F
F
F
F
F
A
A
A
C
A
A
A
A
A
A
A

1926
cro p
r a tin g
C a tk in s

P is t il­
la te
flow ers

Y e a rs
9
Do
Do
Do
Do
Do
Do
Do
Do
Do
Do

____

___
___
___
____

D o ____
D o .....................
D o ................
D o ________
D o _____
D o ____
D o ...................
D o - ..............
D o ________

S U M M A R Y O F A L L V A R IE T IE S

C u rr e n t y e a r ’s crop of—

P r e v io u s y e a r ’s crop of n u t s

A

66 A ’s ...............................................
27 B ’s ...................................... ..
71 C ’s ____ _____ ____________
31 D ' s _____________ _________
29 E ’s ........................................ ..
6 F ’s ...................................... ...........

P is tilla t e flow ers

C a tk in s

5
2
52
16
26
6

B

6
0
13
14
2
0

D

c

7
15
2
1
1
0

E

0
5
3
0
0
0

14
2
0
0
0
0

F

24
3
1
0
0
0

A

10
2
24
12
9
6

B

7
14
23
19
19
0

C

1
4
11
0
1
0

D

F

E

1
I
5
0
0
0

2
2
0
O'
0
0

35
4
8
0
0
0

D ISC U SSIO N

T he general course of developm ent of th e pollen of the pecan is the
sam e as th a t of o th er fruits. T h e fact th a t floral differentiation
occurs a y ea r before th e pollen sheds shows th a t either th e q u an tity
or th e q u ality of pollen m ay be influenced by th e condition of the
trees during th e sum m er, fall, or w inter previous to th e shedding of
pollen. On th e other han d , p istillate flower differentiation occurs
only ab o u t fo u r m onths before the flowers become receptive. T here­
fore i t would be expected th a t th e condition of th e tree during the
previous y ea r would influence stam in ate flower developm ent m uch
more th a n it would p istillate flower developm ent.
Irreg u larities and abnorm alities were found in th e developm ent of
pollen in b o th groups of varieties. In a few cases there were ra th e r
high percentages of defective pollen. H ow ever, in view of the ra th e r
universal abundance of catkin form ation, and therefore of pollen, it
seems unlikely th a t pollen defects or im potence are factors of lm-

110 2

Journal of Agricultural Research

V ol. 40, N o . 12

p o rtan ce in lim iting th e settin g of fru it, except in cases of an isolated
tree or v ariety , and th en only w hen conditions are such as to cause
a failure of sta m in a te flowers to develop.
On th e o th er h an d , th e m ore or less com plete dichogam y th a t
characterizes th e pecan m ay occasion pollination difficulties. T his is
accen tu ated by th e fa ct th a t pollen shedding is p ra ctically in h ib ited
when th e h u m id ity rem ains above a certain po in t for an y considerable
period. I t is still fu rth e r accen tu ated b y th e fa ct th a t th e period of
re cep tiv ity of the stigm as is g reatly reduced if th e w eath er is very
dry. In selecting varieties, therefore, th e question of securing proper
pollination should be considered. F o r p ractical purposes it seems
th a t at least two varieties of each group should be included in a com ­
m ercial planting. T his w ould provide for a t least one v a rie ty to
shed pollen early in th e season and a t least one v a rie ty to shed late.
I t also seems th a t th e n u m b er of trees of eith er of these two v arie­
ties could be reduced to on e-tw en tieth of th e to ta l n u m b er of trees.
SUM M ARY A N D

C O N C L U SIO N

C atk in p rim ordia are differentiated in la te ra l buds on new shoots
th ro u g h o u t the growing season. In varieties of G roup 1, a n th ers are
d ifferentiated in the fall of the y ea r in w hich th e c a tk in prim o rd ia
are form ed; in varieties of G roup 2 an th ers are d ifferen tiated early
the following spring.
No ab n orm al behavior was observed in the d evelopm ent of ca tk in
prim ordia, in d iv idual flower prim ordia, archesporial-cell stage or the
m other-cell stage, b u t abnorm alities occurred in all varieties stu d ied
during the reduction-division stage.
T h e sm ear m eth o d for counting the n u m b er of te tra d s p er an th er,
and the lactic acid m eth o d for determ ining the percen tag e of defective
grains of pollen, have been successfully applied to pecan pollen studies.
A m ethod for q u a n tita tiv e ly catching pollen from th e air a t various
distances from pollen-shedding trees and a t various heights from the
ground was developed.
T h o u g h an entirely satisfacto ry m ethod for g erm inating pecan pollen
has not been developed, m uch was learned ab o u t the te m p e ra tu re ,
h u m id ity , and n u tritio n a l requirem ents for germ in atio n on artificial
m edia. T h e longevity of pollen was found to he ab o u t equal to or less
th a n the period of re cep tiv ity of th e stigm as, w hich in d icates th a t
there m u st be a continuous shedding of pollen th ro u g h o u t the period
of re cep tiv ity of the stigm as.
V! hen 1,000 grains from each of 169 lots of pollen were exam ined
by the lactic acid m ethod, the defective grains were found to range
from 0 to 81.7 per cent. Pollen produced on trees of low vigor or
on trees which bore very heavy crops of catk in s had a slightly higher
percentage of defective grains th a n pollen produced on trees of high
vigor or on trees w hich had a light crop of catkins.
R ecords of bloom ing dates showed th a t eith er hom ogam y, p rc tan d ry , or p ro to g yny m ay occur in pecans.
I t was found th a t pollen sheds only w hen the relativ e h u m id ity of
the air is below ab o u t 85 per cent and th a t p ractically all shedding
occurs betw een 9 a. m. and sundow n.
C onditions which were op tim u m for pollen shedding were d e stru c ­
tive to the v ita lity of pollen. O ptim um conditions for shedding of
pollen are those w hich exist in the o rch ard on a w arm , su n n y d ay ;

June is, 1930 Stam inate Inflorescence and Pollen of Hicoria pecan

1103

and o p tim u m conditions for germ ination are found in an orchard on
a warm , dew y night.
F rom the d a ta contained herein it seems th a t all of the m ethods of
studying pecans w hich involve hand pollination, used by the w riter
and others, have been som ew hat a t fa u lt in th a t account was not taken
of the fact th a t during tim es of low h u m id ity there m ay be an enor­
mous am o u n t of pollen in the air even a t great distances from pollenshedding trees.
T he size of the crop of n u ts of one year was found to influence the
size of crop of b o th stam in ate and pistillate flowers of the following
year. A very heavy crop of n u ts usually follows and is followed by
a lighter crop. C ertain varieties of pecan produce a m edium-size
crop of stam in ate flowers, pistillate flowers, and n u ts each year.
L IT E R A T U R E C IT E D
D . I.

(1

A n d ron escu ,

(2

A n t h o n y , S., and H a r l a n ,
1920. g e r m i n a t i o n o f

(3

A sa m i,

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Mem. Hort. Soc. N. Y. 3: 87-118, illus.
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68 p., illus.
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p h y sio lo g ic a l a sp ects

o f s e lf-s te r ility

o f th e

apple.

Amer.

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, H. E.

K n o w lto n
1922. S T U D I E S

IN

POLLEN

WITH

SPECIAL

REFERENCE

TO

LONGEVITY.

N. Y. Cornell Agr. Expt. Sta. Mem. 52, p. 751-793.

(16

[1925]

POLLEN

ABORTION

IN

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THE

PEACH.

AlllCl'. SoC. Hort. Sci. Pl'OP.

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Journal of Agricultural Research

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1896.

(18)

z u r b io lo g ie d e s p o lle n s .
Jahrb. W iss. B ot. 29: 1-38, illus.
S c h u s t e r , C. E.
1 9 2 4 . F IL B E R T S .
PART I.
G R O W IN G F I L B E R T S I N
OREGON.
PA RT II.
E X P E R IM E N T A L D A T A O N F IL B E R T P O L L IN A T IO N .

(1 9 )

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S h o e m a k e r , J. S .
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to

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(21)

ch ro m o so m e b e h a v io r.

c h e rry

S h u h a rt,

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p o llin a tio n

s tu d ie s .

APPLE,

W IT H

B ot. Gaz.

Oreg. Agr. E xpt.

S P E C IA L

81:

REFERENCE

1 4 8 - 1 7 2 , illu s .

Ohio Agr. E xpt. Sta. Bul. 422,

34 p., illus.
D . V.

THE

M O R P H O L O G IC A L

o f th e

pecan.

D IF F E R E N T IA T IO N

OF

P IS T IL L A T E

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FLOW ERS

illu s .

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G E R M IN A T IO N

TESTS

W IT H

PO LLEN

OF

STO C K S.

JoU T .

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15: 237-243.
H . P.

(23)

S tu c k e y ,
1916.
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1918.
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W. D .
s t e r i l i t y in th e s tr a w b e r r y .

Jour. Agr. Research 12: 613-670,

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W augh,
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(27) ---------1926.

T H E F R U IT -B U D , T H E F L O W E R , A N D T H E N T H E

PECAN N U T.

N atl.

Pecan Growers’ Assoc. Proc. 25: 81-92, illus.
(28)------------and W o o d r o o f , N . C.
1 9 2 6 . F R U IT -B U D D IF F E R E N T IA T IO N A N D S U B S E Q U E N T D E V E L O P M E N T O F
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illus.
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1927. T H E D E V E L O P M E N T O F
flo w e r

TO

THE

m a tu rity .

PECAN

NUT

(H I C O R I A

PECAN)

FROM

Jour. Agr. Research 34: 1049-1063,

illus,
(30)
(31)

— -----

W o o d r o o f , N . C., and B a i l e y , J. E.
1928. u n f r u it f u ln e s s o f t h e p e c a n .
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Amer. Jour. Bot. 15: 416-521, illus.

U. S. G O VE R N ME N T P R I N T I N G O F F I C E : 1 9 3 0