nTHIN WOOD" PRUNING
CONSIDERED FROM THE STANDPOINT OF
PHOTOSYNTHATE PRODUCTION-

T hesis

S u b m i t t e d t o t h e g r a d u a t e f a c u l t y o f t h e M ic h i g a n
S t a t e C o lleg e of A g r i c u ltu r e and A p p lied
Science in p a r t i a l f u l f i l l m e n t of
th e req u ire m e n ts f o r the
D egree o f D o c t o r o f P h i l o s o p h y

by
B a r z i l l a i S. P i c k e t t
1939

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INTRODUCTION
A m ethod of p r u n i n g a p p l e t r e e s o f b e a r i n g ag e
d e v e l o p e d a t t h e M ic h ig a n S t a t i o n by R i c k s a n d G a s to n
a n d d e s c r i b e d by them u n d e r t h e name " t h i n wood" h a s
b e e n e x t e n s i v e l y em ployed and w i t h r a t h e r u n i f o r m l y
successful re s u lts .

I t c o n s i s t s e s s e n t i a l l y i n remov­

in g from t h e t r e e i t s c o m p a r a tiv e ly s l e n d e r o r s o - c a l l e d
" t h i n " b e a r i n g wood a n d i n l e a v i n g i t s t h i c k o r s t o c k y
b e a r i n g wood.

V a r y in g p e r c e n t a g e s o f t h e wood o f i n t e r ­

m e d i a t e c h a r a c t e r a r e r em o v e d , d e p e n d i n g on c o n d i t i o n s .
More s p e c i f i c a l l y t h e c h i e f d i s t i n g u i s h i n g c h a r a c t e r i s t i c s
o f t h e " t h i n " wood a r e :

( l ) b a s a l d i a m e t e r s o f f o u r —y e a r -

o l d g r o w t h s do n o t e x c e e d one—f o u r t h i n c h ,

( 2 ) most o f

t h e s e s l e n d e r b r a n c h e s t e n d t o grow i n a downward d i r e c ­
tio n ,

( 3 ) most o f them a r e f o u n d i n t h e l o w e r an d i n t e r ­

i o r p o rtio n s of the t r e e .

C o n trastin g th ic k ,

stocky

f r u i t i n g b r a n c h e s o f t h e same age a r e t h r e e —e i g h t h s i n c h
o r more i n d i a m e t e r an d a r e f o u n d p r i n c i p a l l y i n t h e
u p p e r and o u t e r p o r t i o n s o f t h e t r e e .

Removal of t h e

s l e n d e r wood a n d r e t e n t i o n o f t h e s t o c k y wood i s recom­
mended i n " t h i n wood" p r u n i n g b e c a u s e o f t h e c l o s e c o r r e ­
l a t i o n f o u n d b e t w e e n s t o c k i n e s s o f b r a n c h an d q u a n t i t y ,
g ra d e and q u a l i t y of f r u i t p ro d u ced .

The d i v i d i n g l i n e s

b e t w e e n t h i n a n d i n t e r m e d i a t e b r a n c h e s an d b e t w e e n i n t e r ­
m e d i a t e a n d t h i c k b r a n c h e s a r e more o r l e s s a r b i t r a r y a n d ,

in a sense a t l e a s t , the reaso n s as w e ll as th e d ir e c ­
t i o n s given f o r th e p ru n in g a re e m p ir ic a l.

The r e l a t i v e

u n i f o r m i t y o f t h e r e s u l t s a t t e n d i n g " t h i n wood" p r u n i n g ,
how ever,

suggest th a t i t

i s a d j u s t e d t o a n d makes u s e o f

b a s i c p r i n c i p l e s of t r e e grow th and n u t r i t i o n .
I t was w i t h t h e o b j e c t i v e i n v ie w of d i s c o v e r i n g why
" t h i n wood" f u n c t i o n s l e s s e f f i c i e n t l y t h a n t h i c k o r
s t o c k y wood t h a t t h i s i n v e s t i g a t i o n was b e g u n .

REVIEW AND DISCUSSION OF
LITERATURE
The l i t e r a t u r e d e a l i n g w i t h p r u n i n g , l i g h t i n r e l a ­
t i o n t o grow th, and p h o to s y n t h e s is ,

i s e x t e n s iv e ^ , y e t

m ost o f t h e m a t e r i a l i s n o t a r r a n g e d t o show t h e i n t e r r e ­
l a t i o n of th e t h r e e .

T h ere a r e many r e f e r e n c e s i n np r u n —

i n g n l i t e r a t u r e to th e im portance of l i g h t a s i t a f f e c t s
p r u n i n g ; n e v e r t h e l e s s , b e c a u s e t h e r e l a t i o n s h i p s seem so
obvious, l i t t l e

d e t a i l e d a t t e n t i o n h a s b e e n g i v e n th e m .

I n t h e i r r e v i e w s a n d d i s c u s s i o n s o f p r u n i n g and I,p r u n i n g n
l i t e r a t u r e A u c h t e r an d Knapp ( l ) ,

C handler ( 5 ), and G ardner,

B r a d f o r d a n d Hooker ($) o f t e n make s t a t e m e n t s i n d i c a t i n g
t h a t l i g h t i s i m p o r t a n t t o g r o w th an d f r u i t p r o d u c t i o n and
g i v e m e th o d s t o improve l i g h t c o n d i t i o n s w i t h i n t h e t r e e
by p r u n in g .

The r e s u l t s e x p e c t e d a r e a n im provem ent i n

t h e d e v e lo p m e n t o f t h e f r u i t i t s e l f a n d i n t h e g r o w t h of
th e in n er branches.
P r u n i n g a s a means o f r e g u l a t i n g t h e amount o f l i g h t
r e a c h i n g t h e l e a v e s on t h e t r e e , a n d so i n f l u e n c i n g g r o w t h ,
h a s h a d v a r i o u s i n t e r p r e t a t i o n s and d i f f e r e n t e x p r e s s i o n s
in p ra c tic e .

Of t h e e a r l i e r A m erican h o r t i c u l t u r i s t s

Downing ( 7 ) seems t o have h a d t h e c l e a r e s t c o n c e p t i o n o f
how l i g h t c o n d i t i o n s w i t h i n t h e t r e e s h o u l d m o d if y p r u n i n g .
He b e l i e v e d t h a t o n l y t h e weak, crow ded b r a n c h e s i n t h e
i n t e r i o r o f t h e t r e e s h o u l d be rem oved.

T h i s t y p e of

p r u n i n g l e a v e s t h o s e b r a n c h e s w hich he c o n s i d e r e d b e s t
-

3-

a d a p t e d t o t h e p r o d u c t i o n of good f r u i t ,
b e s t exposed t o l i g h t .

sin ce th ey are

O ther w r i t e r s a r e of the o p in io n

t h a t no p r u n i n g s h o u l d b e d o n e , s i n c e p r u n i n g g e n e r a l l y
red u ce s y ie ld s of f r u i t .

S t i l l others b eliev e th inn in g

o u t t h e t o p i s t h e b e s t m ethod of p r u n i n g , s i n c e i t p e r ­
m its l i g h t to p a s s through to th e in n e r b ra n c h e s,

Bed­

f o r d a n d P i c k e r i n g ( 3 ) f a v o r t h e n a t u r a l p r u n i n g method
i n w h ic h o n l y d e a d l i m b s an d b r a n c h e s c a u s i n g m e c h a n i c a l
i n j u r y a r e rem o ved.

They p r o v i d e a d e q u a t e d a t a i n s u p p o r t

o f t h i s system .
R i c k s a n d G a s to n ( l 4 ) d i v i d e d t h e a p p l e t r e e i n t o
t h r e e s e c t i o n s w h ich t h e y t e r m e d " t o p " ,
" i n s i d e 11.

11o u t s i d e 1', an d

The " t o p 11 o f t h e t r e e c o n s i s t e d o f t h e b r a n c h e s

m aking up t h e u p p e r 1 /3 o f t h e t r e e ca n o p y ; t h e " o u t s i d e "
was t h a t p a r t o f t h e t r e e canopy below t h e " to p " a n d ex ­
t e n d i n g t o w a r d t h e t r u n k a p p r o x i m a t e l y l / 3 > o r somewhat
less,

o f t h e d i s t a n c e from t r u n k t o b r a n c h t i p s ;

" i n s i d e " was t h e r e m a i n d e r o f t h e t r e e ! s volum e .

and the
They

f o u n d t h a t t h e b r a n c h e s on t h e " i n s i d e " p r o d u c e d p r e d o m i ­
n ately

"U. S. Commercial" g r a d e f r u i t ,

the "o u tsid e"

b r a n c h e s made c h i e f l y "U. S. No. 1" g r a d e a p p l e s , w h i l e
i n t h e " t o p " "U. S. Fancy" g r a d e f r u i t c o n s t i t u t e d t h e
m ajor p o r t i o n of th e c ro p .

An i n v e s t i g a t i o n of t h e t y p e
H

o f f r u i t p r o d u c e d showed t h a t t h e p r e d o m i n a t e g r a d e p r o ­
d u c e d on " t h i n " wood was "U. S. C o m m e r c ia l" , on " i n t e r ­
m e d i a t e " wood "U. S. No. 1 " , a n d on " t h i c k " wood "U. S.

FancyRicks

and Gaston found t h a t ,

in g en eral,

b r a n c h e s w ere f o u n d i n t h e “t o p ” o f t h e t r e e ,

"th ick ”

"in term ed i—

a t e " b r a n c h e s i n t h e " o u t s i d e " and " t h i n " b r a n c h e s aX t h e
'i

"in sid e".

I t i s n o t p o s s i b l e t o draw s h a r p l i n e s o f d e ­

m a r c a tio n , f o r b o th " th ic k " and " in te r m e d ia te " b ra n c h e s
may b e f o u n d i n b o t h " t o p " a n d " o u t s i d e ” p o r t i o n s o f t h e
tree,

the f i r s t p red o m in atin g in th e " to p " , th e l a t t e r

in the "o u tsid e".

S im ilarly ,

some " i n t e r m e d i a t e " wood

may be f o u n d " i n s i d e " t h e t r e e , a l t h o u g h i n d e n s e t r e e s
t h e p r e d o m i n a n t c l a s s i s " t h i n " wood.

The g e n e r a l d i s t r i ­

b u t i o n o f " t h i n " wood i n t h e t r e e s u g g e s t s t h a t i t s d e v e l ­
opment an d g r o w t h m ight be s i m i l a r t o t h a t made by wood
w hich i s i n t e n t i o n a l l y shaded.
The r a n g e o f l i g h t I n t e n s i t i e s , p r o d u c i n g maximum
p h o t o s y n t h e s i s i n h i g h e r p l a n t s was i n v e s t i g a t e d by
B lackm an and M a t t h a e i (4) .

T h e i r e x p e r i m e n t s showed t h a t

t h e r a n g e was fro m .3 9 f u l l s u n l i g h t f o r c h e r r y l a u r e l t o
. 6 9 f u l l s u n l i g h t f o r H e l i a n t h u s t u b e r o s u s a t 27*5° CJ*
P r o b a b l y , a t t h a t t e m p e r a t u r e , maximum p h o t o s y n t h e s i s f o r
t h e a p p l e f a l l s a t some p o i n t b e t w e e n t h e s e two e x t r e m e s .
Hoover ( 1 2 ) , w orking w ith a sm all g r a i n p l a n t , found t h a t
t h e maximum was above 1500 f o o t c a n d l e s .
Popp (13) worked o u t t h e r e l a t i o n b e t w e e n l i g h t a n d
v ig o r in soy-bean s e e d lin g s .

He e x p o s e d s e e d l i n g s t o

l i g h t of d i f f e r e n t i n t e n s i t i e s and f o u n d t h a t , b e t w e e n
26 a n d 4500 f o o t c a n d l e s , v i g o r was d i r e c t l y p r o p o r t i o n a l
to lig h t in te n sity .

"T hin" wood h a s b e e n shown t o p r o d u c e f r u i t w hich
i s f r e q u e n t l y u n d er grade bec au se of sm a ll s i z e and p o o r
co lo r,

S c h r a d e r a n d M a rth ( 1 5 ) made an i n v e s t i g a t i o n o f

t h e d i r e c t e f f e c t o f l i g h t on t h e g r o w t h and c o l o r of
fru it.

They d i d n o t sha de t h e l e a v e s .

I t was f o u n d

t h a t i f l i g h t was r e d u c e d t o .6 1 ^ n o r m a l , o r s l i g h t l y
more t h a n l / 3 >

s i z e was r e d u c e d 2 t o 3 p e r c e n t , a n d t h e

c o l o r of n o r m a l l y r e d f r u i t was r e d u c e d f r o m 96*9 t o
^7.5 p e rc e n t.
G o u r l e y ( 9 ) a n d A u c h t e r (2 ) u s e d a r t i f i c i a l s h a d e ,
e f f e c t e d w i t h s c r e e n s , t h a t f i l t e r e d o u t a b o u t 67 p e r c e n t
o f t h e n o r m a l l i g h t f a l l i n g on a p p l e t r e e s .

M easurement

o f l e a f t h i c k n e s s showed t h e s h a d e d l e a v e s were 53 p e r c e n t
a s t h i c k a s l e a v e s on u n s h a d e d t r e e s .

M i c r o s c o p i c exam~

i n a t i o n showed them t o hav e o n l y one l a y e r o f p a l i s a d e
c e l l s a s com pared t o t h r e e i n u n s h a d e d a p p l e l e a v e s .
S h ad ed wood i n c r e a s e d i n s i z e and i n d r y m a t t e r much
l e s s t h a n d i d u n s h a d e d wood.
T h a t t h e amount of l i g h t w hich i s r e c e i v e d by a p p l e
l e a v e s may v a r y c o n s i d e r a b l y w i t h t h e l o c a t i o n o f t h e
l e a v e s was shown by C h r i s t o p h e r ( 6 ) .
th a t,

He a l s o showed

on d a y s w i t h t h e r e l a t i v e l y h i g h a v e r a g e o f 5000

f o o t c a n d l e s f o r 12 h o u r s ,

l e a v e s on t h e w e s t s i d e of

m a t u r e a p p l e t r e e s r e c e i v e d o n l y enough l i g h t f o r f o u r
h o u r s o f maximum p h o t o s y n t h e s i s ,

C h risto p h er used

1500 f o o t c a n d l e s , t h e f i g u r e s u g g e s t e d by H e i n i c k e , a s
th e b a s is fo r h is c a lc u la tio n s .

6

>’- *

H e i n i c k e and Hoffman ( 1 1 ) , who w orked w i t h t h e
ap p le,

state:

"A mean l i g h t i n t e n s i t y ab o v e 1 5OQ f o o t

c a n d l e s w ould p r o b a b l y s u p p o r t maximum p h o t o s y n t h e s i s
if

o t h e r c o n d i t i o n s w ere f a v o r a b l e " .

L ate r H einicke

( 1 0 ) f o u n d t h a t o v e r a wide r a n g e o f l i g h t i n t e n s i t i e s
a 20 p e r c e n t i n c r e a s e i n i n t e n s i t y r e s u l t e d i n a com­
p a r a b l e i n c r e a s e i n c a r b o n d i o x i d e a b s o r p t i o n 75 p e r c e n t
of th e tim e.

A d e c r e a s e i n t h e l i g h t i n t e n s i t y o f 25

p e r c e n t was a c c o m p a n ie d b y a s i m i l a r d e c r e a s e i n absorp-*
t i o n 70 p e r c e n t o f t h e t i m e .
I t a p p e a r s fro m t h e s e c i t a t i o n s t h a t l i g h t b e lo w
1500 f o o t c a n d l e s may become a l i m i t i n g f a c t o r f o r
p h o t o s y n t h e s i s by ap p le l e a v e s , and c o n s e q u e n tly f o r th e
growth of a p p le b ra n c h e s.

MATERIALS AND METHODS
M aterials:

E x p e r i m e n t s w e r e p e r f o r m e d b o t h a t S o u th

Haven a n d a t E a s t L a n s i n g , M i c h i g a n .

At S o u th Haven

11 G rimes G olden t r e e s 15 y e a r s o l d w ere u s e d , a t E a s t
L a n s i n g 10 t r e e s o f d i f f e r e n t v a r i e t i e s a n d a g e s .
Of t h e t r e e s a t S outh Haven f o u r w ere s e l e c t e d f o r
p h o t o s y n t h e s i s e x p e r i m e n t s b e c a u s e of t h e i r u n i f o r m i t y
and e x c e lle n t p h y sic a l c o n d itio n .

The r e m a i n i n g s e v e n

t r e e s were u s e d f o r g ro w th s t u d i e s and f o r sa m p le s of
" t h i n " an d " t h i c k ' 1 b r a n c h e s and l e a v e s .

The f o u r u n i ­

f o r m t r e e s w ere d i v i d e d i n t o two p a i r s ,

one p a i r p r u n e d

and th e o th e r unpruned.

Of t h e t r e e s a t E a s t L a n s i n g ,

two D uchess o f O ld e n b u r g t r e e s 12 y e a r s o l d , an d a
W in e sa p an d G rim es Golden t r e e 20 y e a r s o l d were u s e d
in the ph o to sy n th esis s tu d ie s .

The o t h e r t r e e s were

u s e d f o r s t u d i e s o f l i g h t and l e a f r e l a t i o n s h i p s .
M ethods:

One h u n d r e d l e a v e s from " t h i n " a n d " t h i c k "

b r a n c h e s o f Grim es Golden a p p l e t r e e s w ere s t u d i e d t o
d i s c o v e r d i f f e r e n c e s i n s t r u c t u r e and f o r m .

The number

o f l a y e r s o f p a l i s a d e c e l l s an d t h e t h i c k n e s s o f t h e
l e a f were d e t e r m i n e d m i c r o s c o p i c a l l y .

The l e n g t h and

t h i c k n e s s o f 50 " t h i n " a n d " t h i c k " o n e - y e a r - o l d s h o o t s
w e re a l s o d e t e r m i n e d f o r c o m p a r a t i v e p u r p o s e s .

S am p lin g

i n t h e s e c a s e s was b a s e d on t h e d i a m e t e r o f t h e b r a n c h e s
a t t h e b a s e o f f o u r - y e a r - o l d wood.
-g-

The r e l a t i o n o f l i g h t t o t h e p r o d u c t i o n o f o r g a n i c
m a t t e r was s t u d i e d by m e a s u r i n g , w i t h a Weston P h o t o e l e c ­
t r i c m e t e r , t h e i n t e n s i t y o f l i g h t f a l l i n g on t h e " t h i c k "
b r a n c h l e a v e s o f a s i n g l e Wine sap t r e e a t t h e b e g i n n i n g
a n d e n d o f t h r e e —h o u r e x p e r i m e n t a l p e r i o d s .

L ight i n t e n ­

s i t y was t r a n s f o r m e d i n t o f o o t c a n d l e h o u r s by m u l t i p l y i n g
th e av erag e l i g h t i n t e n s i t y f o r the e x p e rim e n ta l p e r i o d
by one.

Samples w ere c h o s e n so t h a t t h e y r e c e i v e d fro m

0 t o 3770 f o o t c a n d l e h o u r s o f l i g h t .

I t was n e c e s s a r y

t o s h a d e t h e l e a v e s t o g e t sa m p les f ro m l e a v e s r e c e i v i n g
l e s s t h a n 1000 f o o t c a n d l e h o u r s .

A sam ple o f l e a v e s r e ­

c e i v i n g no l i g h t was t a k e n by b a g g i n g t h e l e a v e s i n t h r e e ­
f o l d brown p a p e r b a g s w h ic h t r a n s m i t t e d o n l y .1 p e r c e n t
of th e in c id e n t l i g h t .

The b a g g e d s a m p le s were a l w a y s

t a k e n on t h e s i d e o f t h e t r e e away fro m t h e s u n ”' .
l e a v e s were u s e d i n e a c h s a m p le .

S ixty

The b a g g e d s a m p l e s w ere

u s e d t o o b t a i n t h e c h a n g e s i n o r g a n i c m a t t e r due t o r e s ­
p i r a t i o n an d t r a n s l o c a t i o n .
The i n t e n s i t y o f l i g h t f a l l i n g on l e a v e s o f " t h i c k "
a n d " t h i n " b r a n c h e s was d e t e r m i n e d by m e a s u r i n g t h e i n t e n ­
s i t y o f l i g h t f a l l i n g on t h e v e n t r a l s i d e o f two h u n d r e d
l e a v e s fro m e a c h b r a n c h c l a s s on 10 d i f f e r e n t t r e e s w h ich
v a r i e d in age, d e n s i t y of f o l i a g e , and v a r i e t y .

R esu lts

a r e e x p re s se d in term s of f o o t ca n d les of l i g h t i n t e n s i t y .
Two s e r i e s o f s a m p le s f o r p h o t o s y n t h e s i s d e t e r m i n a —
*The t e m p e r a t u r e w i t h i n t h e b a g s d i d n o t d i f f e r more t h a n
one d e g r e e fro m a i r t e m p e r a t u r e .
-

9-

t i o n s w ere t a k e n f r o m t r e e s i n t h e S o u th Haven o r c h a r d ,
one s e r i e s fro m t h e p r u n e d t r e e s and t h e o t h e r fro m t h e
unpruned t r e e s .

Samples w ere t a k e n fro m " t h i c k " b r a n c h

spur

a n d s h o o t l e a v e s on a l l t r e e s , a n d f r o m

spur

and s h o o t l e a v e s on t h e u n p r u n e d t r e e s .

were

c o l l e c t e d a p p r o x i m a t e l y e v e r y two w eeks d u r i n g t h e

s p r i n g a n d summer o f 1936.

" t h i n " wood
Sample s

From t h e t r e e s i n t h e E a s t

L a n s i n g o r c h a r d a c o m p o s i t e sample o f s p u r a n d s h o o t
l e a v e s on " t h i c k " b r a n c h e s a n d a s i m i l a r sample f ro m
" t h i n " b r a n c h e s w ere c o l l e c t e d a t t e n - d a y i n t e r v a l s from
J u l y 12 t o A ugust 20, 1937 > fro m e a c h o f t h e f o u r t r e e s
used.
M e a s u r e m e n ts c o m p a r in g " t h i n " an d " t h i c k " l e a v e s
w ere made by t h e " h a l f - l e a f " method d e v e l o p e d by S achs
a n d m o d i f i e d by Ganong.

I t was n e c e s s a r y t o make some

c h a n g e s i n t h e t e c h n i q u e a s d e v e l o p e d by Ganong t o meet
th e l i m i t a t i o n s of apple le a v e s .

B e c a u s e o f t h e numerous

l a r g e v e i n s i n a p p l e l e a v e s , an d b e c a u s e o f t h e i r s m a l l
size i t

i s d i f f i c u l t t o g e t u n i f o r m s a m p le s w i t h t h e

1 cm2 l e a f p u n c h , a n d h e n c e , i n 1 9 3 7 * a s m a l l e r p u n c h ,
c u ttin g discs

.31*14 cm2 , was made and u s e d .

Samples t a k e n

w i t h e i t h e r p u n c h showed t h a t t h e y w ere e q u a l l y s a t i s f a c ­
t o r y when s a m p l i n g was done c a r e f u l l y on l a r g e l e a v e s ”1.
*A s e r i e s o f 15 s a m p le s o f JO d i s c s t a k e n f ro m t h e same
30 a p p l e l e a v e s w i t h i n a p e r i o d o f JO m i n u t e s c o l l e c t e d
w i t h a 1 cm2 p u n c h showed a mean a s h l e s s d r y w e i g h t o f
. 3 0 3 *1- £ .0 0 0 6 gram. A s i m i l a r s e r i e s t a k e n w i t h t h e
.31*14 cm2 p u n c h b u t c o n s i s t i n g of 60 d i s c s t a k e n fro m JO
l e a v e s , h a d a mean w e i g h t , f r e e o f a s h , o f .15 1 5 £ .00 0 2
gram.
—

10 —

S am p le s f o r p h o t o s y n t h e s i s d e t e r m i n a t i o n s were made
a t sundown an d a t s u n r i s e and s u n s e t o f t h e f o l l o w i n g d a y .
A l l o f t h e s a m p l e s w ere p l a c e d i n t a r e d w e i g h i n g b o t t l e s
im m ediately a f t e r c o l l e c t i o n , tak en to th e la b o r a to r y ,
w e i g h e d , d r i e d a t 70° 0 - to** 12 h o u r s , w e i g h e d a g a i n t o ob­
t a i n sam ple d r y w e i g h t an d m o i s t u r e c o n t e n t , and t h e n a s h e d .
The a s h w e i g h t was s u b t r a c t e d from t h e t o t a l d r y w e i g h t t o
g e t t h e o r g a n i c m a t t e r c o n t e n t of t h e s a m p l e s .

The f i r s t

two s a m p le s w ere u s e d t o m e a s u r e m e t a b o l i s m i n t h e d a r k , an d
t h e s e c o n d and. t h i r d s a m p le s t o m e a su re m e t a b o l i s m i n l i g h t
a s i n d i c a t e d by d i f f e r e n c e s i n o r g a n i c m a t t e r c o n t e n t b e t w e e n
th e sam ples.

Tk@ d i f f e r e n c e b e tw e e n s a m p le s 1 and 2 was d i ­

v i d e d by t h e number of h o u r s o f d a r k n e s s an d m u l t i p l i e d by
t h e number of h o u r s b e t w e e n s u n r i s e and s u n s e t t o f i n d t h e
c h a n g e i n o r g a n i c m a t t e r t o be a t t r i b u t e d t o r e s p i r a t i o n a n d
tra n slo c a tio n * .
* I t seemed d o u b t f u l t h a t m e a su r e m e n ts t a k e n a t n i g h t w ould
show m e t a b o l i s m r a t e s h i g h enough t o make t h e i r u s e s a t i s ­
factory.
A c o m p a r i s o n o f s i x b a g g e d s a m p le s t a k e n d u r i n g a
s i n g l e day w i t h an e q u a l number o f s a m p le s made t h e same
n i g h t i s given in th e f o llo w in g t a b l e .
In d iv id u al d if f e r ­
ences are la rg e but the av erag e d if f e r e n c e i s sm a ll.
C o m p a r a t i v e M e t a b o l i s m R a t e s o f A pple L eaves a t 23 ° C. Made
by B a g g in g L ea v es d u r i n g t h e Day, a n d A pple Leaves Open a t
_______ N ig h t w i t h an A v erag e T e m p e r a tu r e o f 17*25° G.__________
Change i n O r g a n i c M a t t e r , Grams
Bagged s a m p l e s , d e t e r ­
Open s a m p l e s , d e t e r m i n a ­
m i n a t i o n s made b e t w e e n
t i o n s made a t n i g h t b e ­
2 and 5
A v er. Temp.
tw ee n s u n s e t a n d s u n r i s e .
23° 0 . T o t a l t i m e : 3
A v e r . Temp. 1 7 .2 5 0 0 .
hours.
T o ta l tim e: 6 h o u r s .
- . 0 0 3^
- . 0 0 2i+
-.0 0 6 2
-.0 0 2 0
-.0 0 5 5
-.0 0 6 ^
.00 12
-.0 0 2 3
-.0 0 3 7
-.0 1 7 6
-.0 0 3 2
-.0 1 1 6
T o ta l w eight
-.0206
-.0*145
A v e r . Sample w t .
—.003^7
- . 007^2
A ver, change p e r h r - .0 0 1 1 6
- .0 0 0 9 2

The d i f f e r e n c e b e t w e e n s a m p le s 2 a n d 3 was c o n s i d e r ­
ed as m etabolism i n l i g h t .

The d i f f e r e n c e b e t w e e n s a m p le s

1 a n d 2 , a f t e r a d j u s t m e n t f o r t i m e , was a d d e d t o t h e above
d i f f e r e n c e and t h e com bined v a l u e was t h e n t e r m e d t h e i n ­
c r e a s e i n o r g a n i c m a t t e r due t o p h o t o s y n t h e s i s * .
*^he u s u a l p r o c e d u r e w i t h t h e " h a l f - l e a f 11 method i s t o u s e
s h o r t i n t e r v a l s of t i m e , o f t e n t w o - h o u r i n t e r v a l s , r a t h e r
th a n th e long i n t e r v a l s used h e re .
For ap p le le a v e s t h i s
i s awkward b e c a u s e t h e l e a v e s v a r y c o n s i d e r a b l y i n t h i c k ­
n e s s fro m t i p t o b a s e , t h e a r e a s n o t i n v a d e d by l a r g e v e i n s
a r e f e w , a n d t h e l e a v e s t h e m s e l v e s s m a l l . Most a p p l e
l e a v e s a r e t o o s m a l l t o a l l o w more t h a n 6 o r 6 cm2 d i s c s t o
b e rem ove d. F o r t h e s e r e a s o n s t h e u s e o f f e w e r t i m e i n t e r ­
v a l s was c o n s i d e r e d more v a l u a b l e p r o v i d e d i t c o u l d be
shown t h a t r e s u l t s n e a r l y l i k e t h o s e o b t a i n e d fro m s h o r t
i n t e r v a l read in g s follow ed.
The t a b l e b elo w i s b a s e d on
d a t a t a k e n f ro m v e r y l a r g e l e a v e s on a Rhode I s l a n d G reen­
i n g t r e e a t S o u th Haven.
Each o f t h e c o m p a r i s o n s i s made
f r o m s e p a r a t e s a m p le s t a k e n a t t h e t i m e s shown.
A C om parison o f t h e S h o r t I n t e r v a l and Long I n t e r v a l Method
o f S am pling f o r Change i n O r g a n ic M a t t e r
Long I n t e r v a l ( S u n s e t , s u n r i s e ,
S u n s e t ) Method
Time
:
C h a n g e, gm.
5 : 4 5 AM :
start

S h o r t I n t e r v a l (2 h o u r )
Method
Change, era.
Time
start
5 : 4 5 AM
.
0081*
7:4-5
. 0011
9:45
.0 1 0 8
11:45
.0051
1:14-5 PM
.0 0 2 6
3:45
.00 99
5: *4-5
.0 0 1 8
7:45
.0018*
9:4-5
.0048*
11:45
. 0112*
1:4-5 am
»• . O I 56
3 : 4 5 AM
5:45
-.0 13 7
T o t a l Change:

.0353

7 :4 5 PM :

.0172

5 :4 5 AM :

-.0 1 7 5
.0347

* S t a r r e d i t e m s c a r r y t h e wrong s i g n s a n d must be s u b t r a c t e d

-

12 -

T w enty-eight p a i r s of branches having n e a rly i d e n t i c a l
d i a m e t e r s a t t h e b a s e o f f o u r - y e a r —o l d wood, a t t h e b a s e o f
o n e - y e a r - o l d wood, n e a r l y i d e n t i c a l g r o w th h a b i t s ,

and h a v ­

i n g t h e same number o f f r u i t s and l e a v e s were c h o s e n f o r
grow th s t u d i e s .

F o u r t e e n p a i r s w ere " t h i n " wood b r a n c h e s

a n d t h e o t h e r s “t h i c k *1 wood.

Growth o f t h e two t y p e s o f

b r a n c h e s was c o m p a r e d on t h e b a s i s o f i n c r e a s e i n b u l k a s
m easured in term s of dry w e ig h t.

One o f e a c h o f t h e 26

p a i r s o f b r a n c h e s was c u t J u l y 21 a n d t h e s e c o n d A ugust
3 , 1936.

The i n c r e a s e s i n b u l k o f t h e new g r o w t h , t h e o l d

w ood, a n d t h e f r u i t w ere r e c o r d e d i n g r a m s .

The l e a f a r e a

was m e a s u r e d , a n d t h e r e l a t i v e p h o t o s y n t h e s i s , e x p r e s s e d
a s gram s o f o r g a n i c m a t t e r p r o d u c e d d u r i n g t h e i n t e r v a l
f o r t h e a v e r a g e l e a f a r e a was r e c o r d e d .

Of t h e 26 p a i r s

o f b r a n c h e s s e l e c t e d 4 p a i r s o f “t h i n " wood b r a n c h e s , a n d
4 p a i r s o f “t h i c k ” wood b r a n c h e s h a d t o be d i s c a r d e d b e ­
c a u s e of l o s s o f f r u i t o r m e c h a n i c a l i n j u r y .

-

13 -

EXPERIMENTAL RESULTS
A com parison of th e p h y s ic a l c h a r a c t e r i s t i c s of
Mt h i c k 1’ a n d " t h i n " b r a n c h e s a n d l e a v e s i s g i v e n i n
T able 1 .

The f o u r t h column c o n t a i n s g e n e r a l i n f o r m a ­

t i o n c o n c e r n i n g b r a n c h e s w h i c h were a r t i f i c i a l l y
b y G o u r l e y (9 ) a n d A u c h t e r ( 2 ) .

shaded

I t i s used to give a

c o m p a r i s o n b e t w e e n " t h i n " wood and s h a d e d wood.
TABLE I
The p h y s i c a l c h a r a c t e r i s t i c s o f " t h i c k ” , " t h i n " , a n d
______ ____
s h a d e d b r a n c h e s _________
O haracteri s ti c
"T h ic k " "T hin" Shaded
D iam eter:
b a s e o f 4- y e a r ~ o l d wood
b a s e o f new t e r m i n a l s h o o t s
L e n g t h o f new t e r m i n a l s h o o t s
I n c r e a s e i n b u l k , 3~yea:i>’0Id.
branches, including f ru it*
T h ick n ess of le a v e s

Layers of p a l i s a d e c e l l s
♦ D u r in g a 1 3 - d a y p e r i o d

.3 8 ”
. 22"
I S .00"

.25"
.15"
A. 0 0 "

weak
short
l e s s than
7.69gra 3-39gm u n s h a d e d
wood
, 20mm . 14mm 53^> l e s s
t h a n un­
shaded
wood
one
2—4
1 -2

D ia m e te r a t b a s e o f 4 - y e a r - o l d wood: (14)
D ia n r e t e r '
a t b a s e o f new t e r m i n a l s h o o t s :
a v e r a g e of ^0 b r a n c h e s .
L en g th o f new t e r m i n a l s h o o t : a v e r a g e o f $ 0
branches.
I n c r e a s e in b u lk of 3-y ear-o ld . b ra n c h e s : a v e r ­
age o f 10 b r a n c h e s .
T hickness of le a v e s :
a v e r a g e o f 100 l e a v e s .
Layers of p a l i s a d e c e l l s :
r a n g e o f 100 l e a v e s .
T h at t h e r e i s a d i f f e r e n c e i n t h e p h y s i c a l c h a r a c t e r ­
istic s

of " t h i n " a n d " t h i c k " wood i s c l e a r l y d e m o n s t r a t e d

-l4 ~

b y o t h e r f e a t u r e s t h a n t h e o n e s by w h ic h R i c k s a n d O ast on
c h o s e t o d e f i n e th e m .

The l e a v e s o f " t h i n " wood a r e much

t h i n n e r t h a n t h o s e o f " t h i c k " wood; t h e i r i n t e r n a l s t r u c ­
t u r e d i f f e r s i n t h a t t h e " t h i n " wood l e a v e s h a v e b u t one
l a y e r o f p a l i s a d e c e l l s a s com pared w i t h t h r e e o r f o u r i n
" t h i c k " wood l e a v e s .

F o u r —month—o l d s h o o t s o f ”t h i c k "

wood g e n e r a l l y h av e g r e a t e r b a s a l d i a m e t e r s an d a r e u s u a l l y
much l o n g e r .
"T hin" wood a n d i n t e n t i o n a l l y s h a d e d wood h a v e s e v e r a l
c h a r a c t e r i s t i c s i n common.
w ea k , n e i t h e r

T erm inal growth i s s h o r t and

" t h i n " wood n o r i n t e n t i o n a l l y s h a d e d wood i n ­

c r e a s e s r a p id ly in s iz e or w eight.

The l e a v e s a r e a b o u t

h a l f a s t h i c k a s t h o s e on b r a n c h e s more f a v o r a b l y e x p o s e d
t o s u n l i g h t , a n d h a v e b u t o n e , i n f r e q u e n t l y tw o, l a y e r s o f
p alisad e c e lls .
B e c a u s e t h e p r o b le m a p p e a r e d t o be a m a t t e r o f l i g h t
relatio n sh ip s,

some e f f o r t was made t o f i n d t h e r e l a t i o n ­

s h i p b e t w e e n t h e p r o d u c t i o n orf o r g a n i c m a t t e r by a p p l e
l e a v e s and t h e l i g h t w hich t h e l e a v e s r e c e i v e d .

Table I I

g i v e s d a t a on t h e p r o d u c t i o n o$ o r g a n i c m a t t e r by t h e
" t h i c k " wood l e a v e s o f a Winesap a p p l e t r e e a s a f f e c t e d by
t h e amount o f l i g h t .
In crease in th e p ro d u ctio n of organic m atter w ith in­
c r e a s e in l i g h t i n t e n s i t y

i s made o b v i o u s by T a b le I I .

The r e l a t i o n s h i p i s c u r v i l i n e a r .
a f t e r t h e m ethod o f l e a s t

The c u r v e o f b e s t f i t ,

s q u a re s, i s t h a t of th e second

degree in the p o t e n t i a l s e r i e s .

T h i s i s shown i n F i g u r e 1,

t o g e t h e r w i t h i t s e q u a t i o n , t h e s t a n d a r d e r r o r o f £ , an d
th e c o e f f ic ie n t of c o r r e la tio n .
The d e g r e e o f c o r r e l a t i o n , r = 0.899&* i s h i g h .

It

f a l l s w ith in th e 5 p e r c e n t p o in t of F is h e r* s t a b l e and i s
cle a rly sig n ific an t.
The s t a n d a r d e r r o r o f £ (&O.3 6 7 ) i s h i g h .

T his i s

a s m ust be e x p e c t e d from an y method f o r t h e s t u d y o f p h o t o ­
s y n th e s is under u n c o n tro lle d c o n d itio n s.
i n p a r t , be e x p l a i n e d by f a t i g u e ,

D e v i a t i o n may,

suddenly changing l e a f

a c t i v i t y because of te m p eratu re or l i g h t v a r i'a tio n , or
o th er v aria b le fa c to rs.
I t i s e v i d e n t t h a t l e a f a c t i v i t y a s m e a s u r e d by t h e
p ro d u c tio n of organic m a tte r i s c lo s e ly r e l a t e d to th e
amount o f l i g h t f a l l i n g on t h e l e a f s u r f a c e .

With t h e

s c o p e o f t h e c u r v e o f " p h o t o s y n t h e s i s " i n mind, i t was
d e s i r a b l e to i n v e s t i g a t e th e r e l a t i o n of l i g h t to the
p r o d u c t i o n o f o r g a n i o m a t t e r by " t h i n " an d " t h i c k " b r a n c h
le av es.

D u rin g t h e summer o f 1937 a g r o u p o f s a m p le s f o r

p h o t o s y n t h e s i s d e t e r m i n a t i o n s were t a k e n a t t h e same t im e
l i g h t m e a s u r e m e n ts were made.

The p r o d u c t i o n o f t h e s e

s a m p l e s , i n t e r m s o f grams p e r s q u a r e m e t e r o f l e a f s u r ­
f a c e p e r h o u r , a v e r a g e d . 7^3 gram a t
hours.

fo o t candle

From t h e f o r m u l a , g i v e n i n Figtxre 1,

" t h i c k " wood

l e a v e s s h o u l d a v e r a g e .8 9 0 gram a t t h i s d e g r e e o f i l l u m i ­
n atio n .

The d i f f e r e n c e o f .107 gram i s o n l y o n e - t h i r d t h e

-

16 -

s iz e of the sta n d a rd e r r o r ,

in d icatin g th a t

" t h i n " wood

le a v e s a re not l e s s e f f i c i e n t p er u n it a re a than "th ic k "
wood l e a v e s .
A ctu al and com parative l i g h t i n t e n s i t i e s r e c e iv e d
b y t h e l e a v e s on t h e " t h i n " a n d " t h i c k " b r a n c h e s o f a p p l e
t r e e s a r e g i v e n i n T a b le I I I .

L ight i n t e n s i t y from th e

su n a n d z e n i t h v a r i e d c o n s i d e r a b l y ,

even on c l e a r d a y s ,

u n d e r M ic h ig a n a t m o s p h e r i c c o n d i t i o n s .

The c o m p a r a t i v e

v a l u e s , t h a t i s , p e r c e n t o f d i r e c t s u n l i g h t , g i v e a more
r e p r e s e n t a t i v e p i c t u r e o f t h e d i f f e r e n c e i n t h e amount o f
l i g h t f a l l i n g on " t h i n " a n d " t h i c k " wood a p p l e l e a v e s t h a n
t h e a b s o l u t e f i g u r e s ; y e t e a c h form o f p r e s e n t a t i o n h a s
c e r t a i n u s e f u l f e a t u r e s w h ich r e q u i r e c o n s i d e r a t i o n .
The i n t e n s i t y o f l i g h t f a l l i n g on " t h i n " wood l e a v e s
v a r i e s more d i r e c t l y w i t h t h e d e n s i t y o f f o l i a g e t h a n w i t h
a n y o t h e r f a c t o r e x c e p t i n t e r f e r e n c e by c l o u d s .

Trees 1

a n d 2 , w h ic h h a d s o m e ' i n t e r m e d i a t e wood? b u t no " t h i n "
wood i n s i d e t h e t r e e ,

r e c e i v e d on t h e l e a v e s o f t h e i n n e r

b r a n c h e s from 1183 t o 1090 f o o t c a n d l e s o f l i g h t b e t w e e n
t h e h o u r s o f 2 and 3 PM on a c l e a r ,

s l i g h t l y h a z y day when

d i r e c t s u n l i g h t a v e r a g e 6955 f o o t c a n d l e s .

The t r e e s o f

g r o u p I I h a d some " t h i n " wood, most of i t n e a r l y l a r g e
en o u g h t o be " i n t e r m e d i a t e " i n c h a r a c t e r .

The l e a v e s on

t h i s wood r e c e i v e d , on t h e a v e r a g e , 390 f o o t c a n d l e s o f
l i g h t , w h i l e t h e " t h i c k " wood l e a v e s o b t a i n e d 3152 f o o t
c a n d l e s d u r i n g a p e r i o d when d i r e c t s u n l i g h t was a p p r o x i ­
m a t e l y 8528 f o o t c a n d l e s .

The o l d e r t r e e s ,

-

17 -

in group I I I ,

h a d a l a r g e amount o f " t h i n " wood, some o f i t e x t r e m e l y
"th in "

in type.

L ea v es on t h e " t h i n " wood i n t h e s e c a s e s

a v e r a g e d 14-2 f o o t c a n d l e s o f l i g h t when t h e mean i n t e n s i t y
of d ire c t
leav es

s u n l i g h t was 8339 f o o t c a n d l e s . " T h i c k ” wood

on t r e e s o f t h i s g r o u p r e c e i v e d a n a v e r a g e o f 3 1$&

fo o t can d les of l i g h t .
Use o f some o f t h e s e l i g h t v a l u e s i n t h e e q u a t i o n o f
F i g u r e 1 i n d i c a t e s t h a t " t h i n " wood l e a v e s may p r o d u c e , a t
109 f o o t c a n d l e s ,

. 3 7 *+ gram o f o r g a n i c m a t t e r p e r h o u r ,

a n d a t 428 f o o t c a n d l e s t h e y may p r o d u c e -75& gram p e r h o u r * .
The r e l a t i v e v a l u e s a r e s i m i l a r t o t h o s e o f Blackman
a n d M a t t h a e i ( 4 ) , e x c e p t t h a t Blackman u s e d a s h i s v a l u e f o r
f u l l s u n l i g h t t h e maximum amount of l i g h t r e c e i v e d from t h e
sun.

The c o m p a r a t i v e v a l u e s g i v e n i n T a b le 3 a r e o b t a i n e d

b y d i v i d i n g t h e a v e r a g e amount o f l i g h t f a l l i n g on l e a v e s
by t h e d i r e c t s u n l i g h t i n t e n s i t y a t t h e t i m e r e a d i n g s were
tak en .

The " t h i n " wood l e a v e s on t h e t r e e s o f g r o u p I I r e ­

c e i v e d .0 4 6 f u l l s u n l i g h t , and t h o s e o f g r o u p I I I

.017*

The a v e r a g e amount o f l i g h t r e c e i v e d by " t h i c k " wood l e a v e s
on a l l o f t h e t r e e s i n t h e s e two g r o u p s was *374 f u l l su n ­
lig h t.

From t h e f o r m u l a f o r t h e p r o d u c t i o n o f o r g a n i c

m atter

a s r e l a t e d t o t h e amount of l i g h t , maximum p h o t o s y n ­

th esis

a t a b o u t 23° 0 . w ould o c c u r w i t h .4 39 f u l l s u n l i g h t .

S i n c e Blackman a n d M a t t h a e i show t h a t maximum p h o t o s y n t h e s i s
( a t 2 7 *5° C .) r e q u i r e s f ro m .3 6 t o .6 9 f u l l s u n l i g h t i t
♦The s t a n d a r d e r r o r o f t h e s e f i g u r e s i s A .3 6 7 gram .

is

evident th a t

" t h i n " wood l e a v e s , w h ic h r e c e i v e on t h e a v e r ­

age l e s s th a n .0 4 f u l l s u n l i g h t , cannot be v e r y a c t i v e i n
th e p r o d u c tio n of p h o to s y n th a te .
The d a t a so f a r d i s c u s s e d h a v e b e e n l i m i t e d w i t h r e s ­
p e c t t o t i m e an d by some a r b i t r a r y r u l e s o f p r o c e d u r e .

It

r e m a i n s , t h e n , t o f i n d w h e t h e r o r n o t " t h i n 11 wood a n d " t h i c k "
wood l e a v e s a n d b r a n c h e s w i l l r e a c t i n t h e same f a s h i o n o v e r
a l o n g p e r i o d o f t i m e , d u r i n g w hich e n t i r e d a y s a r e c o n s i d e r ­
e d r a t h e r t h a n i n t e r v a l s o f a few h o u r s .

The r e s u l t s o f t h i s

s t u d y a r e g i v e n by T a b l e s 4 an d 5> w h ic h w i l l be s e p a r a t e l y
co nsid ered.

T a b l e 4 shows t h e r e s u l t s o f t h e 1936 s e a s o n an d

T a b l e 5 “t h o s e o f 1937-

T a b l e 4 i s so a r r a n g e d t h a t c o m p a r i­

s o n s may b e made b e t w e e n l e a v e s fro m s p u r s an d s h o o t s on
" t h i n " a n d " t h i c k " wood on b o t h p r u n e d a n d u n p r u n e d t r e e s .
It

i s n o t i c e a b l e t h a t e v e r y s e r i e s o f s a m p le s v a r i e d w i d e l y

f r o m t h e mean r e s u l t ;

y e t i n few c a s e s d i d " t h i n " wood l e a v e s

e q u a l o r e x c e e d t h e p r o d u c t i o n o f o r g a n i c m a t t e r by " t h i c k "
wood l e a v e s .
The e x t r e m e s o f p r o d u c t i o n by " t h i c k " wood l e a v e s a r e
1 5 . 8 7 gram s p e r s q u a r e m e t e r o f l e a f s u r f a c e a s t h e maximum
a t t a i n e d , a n d - 8 .0 7 a s t h e minimum, t h e a v e r a g e b e i n g 5 .3 6
gram ^per day.

F o r " t h i n " wood l e a v e s t h e e x t r e m e s a r e

7 . 0 0 a n d - 1 6 .2 0 g r a m s , r e s p e c t i v e l y , f o r t h e maximum a n d
minimum p r o d u c t i o n , w h i l e t h e a v e r a g e f o r t h e 90- d a y p e r i o d
was —O.3 8 gram.

" T h ic k " wood l e a v e s on u n p r u n e d t r e e s

av e ra g ed s l i g h t l y h ig h e r in p ro d u ctio n of organic m a tte r

o v e r t h e 9 0 - d a y p e r i o d t h a n d i d t h e same t y p e o f l e a v e s on
pruned tr e e s .

On u n p r u n e d t r e e s a l l “thick** wood l e a v e s

a v e r a g e d 6 . 0 2 gram s o f o r g a n i c m a t t e r p e r s q u a r e m e t e r o f
l e a f s u r f a c e p e r d a y ; on p r u n e d t r e e s t h e l e a v e s p r o d u c e d
an a v e ra g e of 4 .7 1 grams.
In o rd e r to i l l u s t r a t e th e course of organic m a tte r
p r o d u c t i o n d u r i n g t h e p e r i o d of t h e e x p e r i m e n t , a n d t o com­
p a r e t h e r a t e a t w h ic h e a c h t y p e o f l e a f i s a b l e t o make
o r g a n i c m a t t e r , F i g u r e 2 was d e v e l o p e d .

T h i s g r a p h shows

t h e sum m ation c u r v e s f o r t h e p r o d u c t i o n o f o r g a n i c m a t t e r
b y " t h i n 11 a n d “t h i c k * 1 wood l e a v e s a s t h e y a p p e a r , when
d e v e l o p e d i n t h e f o l l o w i n g manner:

The d a i l y p r o d u c t i o n

f o r e a c h two s u c c e s s i v e r e a d i n g s was a v e r a g e d , m u l t i p l i e d
b y t h e number o f i n t e r v e n i n g d a y s , a n d t h e t o t a l s a d d e d
su ccessiv ely .

I t w i l l be s e e n t h a t f o r a b o u t JO d a y s f o l ­

l o w i n g J u n e 5 “thin** wood l e a v e s , i n g e n e r a l ,
apparent photosynthesis*.
w ere a c t i v e .

showed no

A f t e r J u l y 8 “t h i n 11 wood l e a v e s

C o m p a r iso n s o f y i e l d s o f o r g a n i c m a t t e r by

t h e two t y p e s o f l e a v e s w ere made by d r a w in g a s t r a i g h t
l i n e f ro m t h e p o i n t o f o r i g i n t o t h e end p o i n t of t h e c u r v e ,
and d e te rm in in g th e slope of th e l i n e .

B e ca u se o f t h e

n a t u r e o f t h e c u r v e f o r **thin‘! wood a s drawn fro m t h e 1936
d a t a , a n d shown i n F i g u r e 2 , two l i n e s were draw n,

fro m

t h e p o i n t o f o r i g i n t d a p o i n t 33 d a y s o u t on t h e X a x i s
a l o n g B, a n d Cg fro m t h i s p o i n t t o t h e en d p o i n t o f t h e
* R e f e r e n c e t o T a b l e 4- w i l l show t h a t t h i s i s n o t i n v a r i a b l y
th e case.
-

20 -

su m m a tio n c u r v e .

The amount o f o r g a n i c m a t t e r w h ic h w a s

m a n u f a c t u r e d , b y • ' t h i c k 11 wood l e a v e s f o r e a c h gram u s e d o r
p r o d u c e d by " t h i n " wood l e a v e s was c a l c u l a t e d by d i v i d i n g
th e slop e of th e l i n e re p re s e n tin g th e p ro d u ctio n of "th ick "
wood l e a v e s by t h e s l o p e o f l i n e w i t h w h ic h i t was t o be
com pared.
of

F o r e x a m p le , t h e s l o p e o f

d i v i d e d by t h e s l o p e

shows t h a t f o r e a c h gram o f o r g a n i c m a t t e r p r o d u c e d

b y " t h i n " wood l e a v e s f o r t h e 90- d a y p e r i o d " t h i c k " wood
l e a v e s m a n u f a c t u r e d 1 2 .9 g r a m s .
From J u n e 5 t o J u l y g " t h i n " wood l e a v e s must h a v e r e ­
c e i v e d fro m t h e t r e e o r b r a n c h , on t h e a v e r a g e , 1 gram f o r
e a c h 3*^5 grams o f o r g a n i c m a t t e r made b y t h e " t h i c k " wood
leaves,

b o r in g th e l a t t e r p a r t of th e e x p e rim e n ta l p e r io d

" t h i n " wood l e a v e s m a n u f a c t u r e d 1 gram o f o r g a n i c m a t t e r
f o r e v e r y 3*32 gram s p r o d u c e d by " t h i c k " wood l e a v e s .
The q u e s t i o n o f w h e t h e r o r n o t " t h i n " wood i s a c t u a l l y
p a r a s i t i c may be c o n s i d e r e d from two v i e w p o i n t s on t h e b a s i s
o f t h e d a t a shown.

F irst,

view ed, i t a p p e a rs t h a t

i f t h e d a t a i n T ab le k a r e r e ­

" t h i n " wood c o u l d be p a r a s i t i c

t h e a v e r a g e u n w e i g h t e d d a i l y p r o d u c t i o n i s —Q.3& g ram .

since
The

t a b l e does not ta k e tim e i n t o c o n s i d e r a t i o n a s th e g ra p h s
i n F ig u r e 1 do.

From J u n e 5 t o J u l y

" t h i n " wood was n o t

m a k in g o r g a n i c m a t t e r a s f a s t a s i t was b e i n g u s e d , a n d a t
t h i s t i m e t h e r e i s a p o s s i b i l i t y t h a t t h e wood was n o t s e l f supporting.

From J u l y g t o S eptem ber 3 t h e p r o d u c t i o n o f

o r g a n i c m a t t e r by t h e " t h i n " wood l e a v e s on t h e s e same t r e e s
e x c e e d e d by l M i .3 grams t h e amount t h a t was l o s t d u r i n g t h e

—21—

f i r s t p a r t o f t h e e x p e r i m e n t a l p e r i o d , i n d i c a t i n g t h a t " t h i n 11
wood was n o t e n t i r e l y p a r a s i t i c ,

i f a t a l l so.

The d a t a c o l l e c t e d i n 1937 d e f i n e more e x a c t l y t h e e x t e n t
o f t h e d i f f e r e n c e i n o r g a n i c m a t t e r p r o d u c t i o n by " t h i n " and
" t h i c k " wood l e a v e s .

The e x t r e m e s o f p r o d u c t i o n , a s shown i n

T a b l e 5 w ere f o r 11t h i c k '1 wood l e a v e s 1 3 .0 9 grams a n d I .5 0
gram s a s c o m p ared w i t h a maximum o f 3*^7 grams and a minimum
o f - 1 . 1 1 gram s p e r s q u a r e m e t e r o f l e a f s u r f a c e p e r d a y f o r
11t h i n " wood l e a v e s .

The a v e r a g e p r o d u c t i o n f o r " t h i c k " wood

l e a v e s was 6 . 3^ grams a s com pared w i t h 1 .6 6 grams f o r t h e " t h i n . "
C o m p a r is o n s ( F i g u r e 3 ) were made b e t w e e n t h e r e l a t i v e
am ount o f l i g h t r e c e i v e d by " t h i c k " an d " t h i n " wood l e a v e s
on t h e s e t r e e s .

" I n t e r m e d i a t e " wood l e a v e s on Duchess t r e e

No. 1 l o c a t e d " i n s i d e "

t h e t r e e r e c e i v e d . 15$ t h e amount

o f l i g h t f a l l i n g d i r e c t l y from t h e s u n .

T hese l e a v e s p r o ­

d u c e d .2 7 a s much o r g a n i c m a t t e r a s d i d t h e " t h i c k " wood
l e a v e s o r a n a v e r a g e o f 2 .3 5 grams o f o r g a n i c m a t t e r p e r
day.

" T h in " wood l e a v e s on Duchess t r e e No. 2 r e c e i v e d

.0 5 f u l l s u n l i g h t ; y e t t h e y p r o d u c e d a d a i l y a v e r a g e o f
1 . 9 2 gram o f o r g a n i c m a t t e r p e r s q u a r e m e t e r o f l e a f s u r ­
f a c e p e r day w h i c h was .3 5 t h e amount p r o d u c e d by " t h i c k "
wood l e a v e s on t h e same t r e e .

The " t h i n " wood l e a v e s on

t h e Wine sa p t r e e r e c e i v e d .0 2 1 f u l l s u n l i g h t and. made .2 3
a s much o r g a n i c m a t t e r a s t h e " t h i c k " wood l e a v e s o r a n
a v e r a g e o f 1 .^ 2 gram o f o r g a n i c m a t t e r p e r d a y .

Grimes

G-olden " t h i n " wood l e a v e s r e c e i v e d .0 1 2 f u l l s u n l i g h t a n d

-2 2 -

p r o d u c e d .2 2 a s much o r g a n i c m a t t e r a s t h e " t h i c k " wood
l e a v e s on t h e same t r e e o r a d a i l y a v e r a g e p r o d u c t i o n o f
• 93 gram p e r s q u a r e m e t e r o f l e a f s u r f a c e p e r day b e t w e e n
J u l y 13 a n d A u g u st 2 0 , 1937"th in "

This te n d s to i n d i c a t e t h a t

l e a v e s may b e from s l i g h t l y below e q u a l l y e f f i c i e n t

t o more t h a n t h r e e t i m e s a s e f f i c i e n t p e r u n i t o f l i g h t
r e c e i v e d p e r u n i t o f l e a f a r e a a s " t h i c k " wood l e a v e s .
H ow ever, i t i s a p p a r e n t t h a t much more t i m e i s r e q u i r e d
f o r th e m t o p r o d u c e an e q u a l amount o f o r g a n i c m a t t e r .
Even t h e

" i n t e r m e d i a t e " l e a v e s on D uchess t r e e No. 1 w ould

r e q u i r e 2 . 7 t i m e s a s l o n g t o p r o d u c e t h e amount o f o r g a n i c
m a t t e r p r o d u c e d by t h e a v e r a g e f o r a l l

" t h i c k " wood l e a v e s .

A c o m p a r i s o n was made b e tw e e n t h e a v e r a g e summation
c u r v e s f o r " t h i n " and " t h i c k " wood l e a v e s f o r t h e d a t a c o l ­
l e c t e d i n 1937 s i m i l a r t o t h a t made fro m t h e d a t a o f 193&*
I t was f o u n d t h a t b e t w e e n J u l y 13 an d A ugust 20 " t h i c k "
wood l e a v e s p r o d u c e d 3*5 g^ams f o r e a c h gram made by " t h i n "
wood l e a v e s ( F i g u r e M-).
I f t h e l e a v e s on " t h i n " wood a r e l e s s a b l e t o make
fo o d f o r b ran ch and f r u i t growth, th e b r a n c h e s , a s w e ll a s
th e f r u i t ,

must s u f f e r from t h e l a c k .

T here s h o u l d be some

r e l a t i o n b e t w e e n t h e amount o f o r g a n i c m a t t e r p r o d u c e d by
p h o t o s y n t h e s i s a n d t h e amount l a i d down i n t h e b r a n c h e s
d u r i n g th e growing se aso n .

A c o m p a r is o n o f t h e amount o f

g r o w t h ma.de by " t h i n " and " t h i c k " b r a n c h e s , and t h e amount
o f o r g a n i c m a t t e r w h ic h t h e l e a v e s c o u l d have p r o d u c e d a t
t h e same t i m e i s p r e s e n t e d i n T ab le 6 #

-2 3 -

P e r u n i t o f l e a f a r e a " t h i n *1 wood l e a v e s made a b o u t
11 p e r c e n t a s much o r g a n i c m a t t e r a s d i d ‘’t h i c k 11 wood
l e a v e s , a n d t h e b r a n c h e s i n c r e a s e d k-J p e r c e n t a s much i n
b u l k d u r i n g t h e i n t e r v a l shown b y T a b le 6 .

A ssum ing,

how ever, t h a t r e s p i r a t i o n o f l e a v e s , b r a n c h e s and f r u i t
r e q u i r e d 20 p e r c e n t o f t h e m a n u f a c t u r e d o r g a n i c m a t t e r ,
a s su g g e ste d by H einicke ( 1 1 ),
a little
down.

" t h i n ” wood l e a v e s p r o d u c e d

more t h a n t w i c e t h e amount o f d r y m a t t e r l a i d

U nder t h e c o n d i t i o n s o f t h i s e x p e r i m e n t “t h i n ” wood

w as n o t p a r a s i t i c ,

f o r o b v i o u s l y t h e l e a v e s w ere f u l l y

c a p a b l e o f s u p p o r t i n g t h e b r a n c h e s and s u p p l y i n g s u f f i c i e n t
e l a b o r a t e d m a t e r i a l s t o a c c o u n t f o r b r a n c h m a i n t e n a n c e and
t h e s m a l l g r o w t h made.
lary ,

th at

I t i s eq u ally evident th a t the corol

“t h i n ” wood makes l i t t l e

g ro w th b e c a u s e i t

s u p p li e d w ith sm all q u a n t i t i e s of e la b o r a te d food,

2

^I

■ -*

is

is tru e.

CONCLUSIONS
S i n c e g r o w t h i s l i m i t e d by t h e amount o f f o o d a n d
f o o d m a t e r i a l s w h ic h t h e b r a n c h e s o b t a i n fro m t r e e * and
leaf i t

i s a p p a r e n t t h a t t h e s i z e and d e v e lo p m e n t o f f r u i t

a n d b r a n c h w i l l b e l i m i t e d by t h e q u a n t i t y o f e i t h e r w h ic h
th e branch i s ab le to o b ta in .

The amount o f e l a b o r a t e d

p l a n t f o o d w h ic h t h e b r a n c h e s w i l l g e t from t h e l e a v e s on
t h e m i s m o d i f i e d by t h e q u a n t i t y o f l i g h t w h ic h t h e l e a v e s
receiv e.

Since r e l a t i v e l y l i t t l e

l i g h t f a l l s on “t h i n ”

wood l e a v e s t h e amount o f e l a b o r a t e d p l a n t f o o d w h ic h t h e
b r a n c h e s w i l l g e t w i l l be much l e s s t h a n i s p r o d u c e d by
t h e more s t r o n g l y i l l u m i n a t e d “t h i c k 11 wood b r a n c h e s .
The s i z e o f f r u i t b o r n e on “t h i n ” wood b r a n c h e s i s
s u b j e c t t o two a d v e r s e f a c t o r s , t h e f i r s t b e i n g t h e f a c t
t h a t t h e a v a i l a b l e supply of e l a b o r a t e d food w i l l be sm a ll,
a n d t h e se c o n d t h a t l e s s l i g h t f a l l s on t h e f r u i t i t s e l f .
F r u i t on wood w h ic h o b t a i n s fro m l e s s t h a n 6 p e r c e n t t o
n o t more t h a n 4-3 p e r c e n t a s much l i g h t a s f r u i t on “t h i c k ”
b r a n c h e s w i l l be s m a lle r in s iz e f o r t h i s r e a s o n .

In addi­

t i o n , t h e g r a d e o f t h e f r u i t w i l l be r e d u c e d b e c a u s e , f r u i t
s o p o o r l y i l l u m i n a t e d w i l l n o t b e so w e l l c o l o r e d .
W i th r e f e r e n c e t o p r u n i n g a s a means o f i n f l u e n c i n g
t h e f r u i t i n g h a b i t o f t r e e s an d t h e ec o n o m ic s o f f r u i t
♦The o t h e r p o s s i b l e r e a s o n f o r t h e d e v e lo p m e n t o f “t h i n ”
w ood,— t h a t i s , the r e s t r i c t e d en tra n c e o f food m a t e r i a l s
f r o m t h e r e m a i n d e r o f t h e t r e e , i s p r o b a b l y a m inor c a u s e
s i n c e i t i s d e p e n d e n t upon s e v e r e m e c h a n i c a l o r p a t h o l o g i ­
c a l i n ju r y , senescence, or poor s o i l c o n d itio n s .
-2 5 -

p r o d u c t i o n t h e r e s u l t s t h a t h a v e b e e n p r e s e n t e d o f f e r some
v alu a b le su g g estio n s.

A common p r u n i n g p r a c t i c e t o im prove

t h e grow th of f r u i t and b ra n c h i s " th i n n i n g o u t" , t h a t i s ,
c u t t i n g o u t some o f t h e ca n o p y b r a n c h e s so t h a t l i g h t may
p e n e t r a t e d e e p e r tow ard th e t r e e t r u n k .
i n g re m o v e s much good f r u i t i n g wood.

T his ty p e o f prim ­

I f p r u n i n g by t h i s

m e th o d c o u l d r a i s e t h e l e v e l o f l i g h t r e a c h i n g t h e i n n e r
b r a n c h e s t o t h a t w h ic h r e a c h e s t h e l e a v e s on t h e b r a n c h e s
m a k i n g up t h e t r e e c a n o p y , t h e l e a v e s on t h e b r a n c h e s " i n s i d e "
th e t r e e could produce, t h e o r e t i c a l l y ,

e q u a l l y good f r u i t

a f t e r v ig o r o u s growth had been r e - e s t a b l i s h e d .

However, i t

w as o b s e r v e d t h a t a t b e s t n o t more t h a n M-3 p e r c e n t a s much
l i g h t c o u l d b e e x p e c t e d t o f a l l on t h e i n n e r b r a n c h l e a v e s
o f h e a l t h y , v i g o r o u s , open t r e e s a s f e l l on t h e canopy b r a n c h
leaves.

C o n s e q u e n t l y , t h e i n v i g o r a t i o n o f weak w ood,— making

t h i c k , p r o d u c t i v e f r u i t i n g b r a n c h e s out o f " t h i n " o n e s — i s
im p racticab le.

The n o r m a l c o u r s e i s f o r s t o c k y wood t o b e ­

come w e a k e r , f o r " t h i c k " t o a c q u i r e t h e c h a r a c t e r i s t i c s o f
" t h i n " wood, a s i t becomes o l d e r , due i n l a r g e m e asure t o
shading.

T h i s t e n d e n c y c a n n o t be. r e v e r s e d b e c a u s e i t i s t h e

v e r y n a t u r e of t r e e s

(a s opposed to sh ru b s) to produce t h e i r

s t r o n g e s t new g r o w t h from t h e i r o u t e r a n d u p p e r e x t r e m i t i e s .
From t h e s t a n d p o i n t o f o r c h a r d e c o n o m ic s , t h e n , i t

is

e v i d e n t t h a t t h e r e m o v a l o f b r a n c h e s w h ic h make up t h e t r e e
canopy i s n o t th e answer t o p r o f i t a b l e p ro d u c tio n f o r , w ith
no p r u n in g ,

it

i s t h e s e b r a n c h e s w hich r e c e i v e t h e most

l i g h t a n d make t h e b e s t f r u i t .

The i n n e r b r a n c h e s w h ich

p r o d u c e t h e p o o r e s t f r u i t an d make t h e l e a s t g r o w t h can
b e re m o v e d a d v a n t a g e o u s l y s i n c e such p r u n i n g r e d u c e s t h e
n um ber o f p o o r s p e c i m e n s w h ic h must be p i c k e d , h a n d l e d
and m arketed.

Of t h e v a r i o u s m e thods o f p r u n i n g f o r t h e

p u rp o s e of im proving th e q u a l i t y of th e f r u i t h a r v e s te d ,
" t h i n " wood p r u n i n g makes t h e g r e a t e s t u s e o f t h e i n t e r p r e t a ­
t i o n s b a s e d on t h e d a t a o b t a i n e d by t h e s e e x p e r i m e n t s i n
p h o to sy n th esis.

-2 7 -

SUMMARY
E x p e r i m e n t s which, were a im e d t o d e t e r m i n e how d i r e c t l y
t h e t h e o r y t h a t c e r t a i n b r a n c h e s of t h e a p p l e t r e e a r e " t h i n "
b e c a u s e t h e y a r e p o o r l y n o u r i s h e d m ig h t be a p p l i e d w ere made
w ith th e fo llo w in g r e s u lt s :
1.

On " t h i c k " wood l e a v e s i t was f o u n d t h a t l i g h t a f ­

f e c t e d th e p r o d u c tio n of o rg a n ic m a tte r a c c o rd in g t o th e
r e l a t i o n s h i p , Y = 0 .2 3 5 2
^tO.3 6 7 .

1232X;— 0 .0 0 1 4 6 X2 , w i t h Sy =

L i g h t was c o r r e l a t e d w i t h p r o d u c t i o n t o t h e e x t e n t

r Yl = 0 . 3 9 9 $ .
2.

" T h in " wood l e a v e s r e c e i v e d f ro m .017 t o .0 5 f u l l

s u n l i g h t a s c o m p ared w i t h f ro m .23 t o .465 f o r " t h i c k " wood
l e a v e s , b u t were a p p a r e n t l y e q u a l l y e f f i c i e n t p e r u n i t l e a f
a r e a , per u n it of lig h t receiv ed .
3.

Two y e a r s o f e x p e r i m e n t s a t t e m p t i n g t o d e t e r m i n e

t h e a p p r o x i m a t e amount o f o r g a n i c m a t t e r w h ic h " t h i n " and
" t h i c k " wood l e a v e s c o u l d p r o d u c e p e r a v e r a g e day showed
t h a t " t h i n " l e a v e s c o u l d p r o d u c e f ro m —1 . 3 2 t o 2 . 3 5 grams
w h e r e " t h i c k " wood l e a v e s c o u l d p r o d u c e from 4 . 1 9

3.31

gram s p e r s q u a r e m e t e r o f l e a f s u r f a c e p e r day u n d e r a v e r ­
age grow ing se a so n c o n d i t i o n s i n s o u th e rn M ichigan.
4.

" T h in " b r a n c h e s d i d n o t i n c r e a s e i n b u l k a s r a p i d l y

a s " t h i c k " b r a n c h e s b u t t h e l e a v e s on " t h i n " b r a n c h e s were
a p p a re n tly able to p ro v id e, g e n e ra lly ,

enough o r g a n i c m a t t e r

t o a c c o u n t f o r a n y g a i n i n b u l k w h ich t h e y made.

-2 3 -

I t i s c o n c lu d ed , t h a t
sitic ,

“t h i n 11 b r a n c h e s a r e n o t p a r a ­

e x c e p t u n d e r t h e most e x t r e m e c o n d i t i o n s , b u t

t h a t beca,use t h e i r l e a v e s do n o t r e c e i v e s u f f i c i e n t
lig h t,

th e y a r e l e s s w e ll n o u r is h e d and c o n s e q u e n tly ,

11t h i n n e r 11 t h a n t h e o t h e r b r a n c h e s on t h e t r e e .

F u rth er­

m o r e , on t h e b a s i s o f t h e s e d a t a , a n d i n t h e l i g h t o f t h e
w ork r e v i e w e d ,

" t h i n " wood f r u i t w i l l b e l e s s w e l l c o l o r e d

( i f commonly r e d ) a n d s m a l l e r i n s i z e t h a n f r u i t on o t h e r
branches.
W ith r e s p e c t t o p r u n i n g t h e c o n c l u s i o n s drawn are
th a t

it

i s b e t t e r t o remove t h e wood b e a r i n g p o o r f r u i t

r a t h e r t h a n t o a t t e m p t t o im p ro v e t h e g r o w t h o f t h e weak
11t h i n " b r a n c h e s by r e m o v in g good f r u i t i n g wood fro m t h e
o u t e r p a r t o f t h e t r e e c a n o p y , “ t h e same r e c o m m e n d a t i o n s
a s t h o s e made by R i c k s a n d G a s t o n i n t h e i r “t h i n ” wood
method of p r u n i n g .

-2 9 '

ACKNOWLEDGMENTS
The w r i t e r w i s h e s t o t a k e t h i s o p p o r t u n i t y t o ex­
p r e s s h i s a p p r e c i a t i o n t o t h e South Haven O r c h a r d Company
f o r t h e u s e o f t h e i r o r c h a r d ; t o Mr. S t a n l e y J o h n s o n ,
s u p e r i n t e n d e n t o f t h e S o u th Haven E x p e r im e n t S t a t i o n f o r
h i s h e l p and h i s l a b o r a t o r y ;

t o P r o f . V. K. G a r d n e r , an d

t o D r . J o h n W. C r i s t o f t h e D e p a rtm e n t o f H o r t i c u l t u r e ,
f o r many h e l p f u l s u g g e s t i o n s a n d c r i t i c i s m s d u r i n g t h e
p r o g r e s s o f t h e work a n d i n t h e p r e p a r a t i o n o f t h e p a p e r .

-3 0 -

LITERATURE CITED
1.

A u d i t e r , E. C. and Knapp, H. B* O r c h a r d an d S m all
F ru it C ulture.
T hird e d i t i o n .
Jo h n W iley & S ons,
Inc.
New York.
1 937 .

2.

A u c h t e r , E. C . , S c h r a d e r , A. L ee, F a g a s s e , T. S. a n d
A l d r i c h , W. W. The E f f e c t o f Shade on t h e G rowth,
F r u i t Bud F o r m a t i o n a n d C he m ic al C o m p o s i t i o n o f
A pples.
P r o c . Amer. S oc. H o r t . S c i . 2 ^ : 3 6 6 .
1926.

3-

B e d f o r d , Duke o f , a n d P i c k e r i n g , S. U. S c i e n c e a n d
F r u i t G ro w in g . M a c m i l l a n & Co.
London. 19 19.
B l a c k m a n , F . F . and M a t t h a e i , G. L. C. Optima an d
L im iting F a c to rs .
Ann. B o t . 1 9 : 2 6 1 - 2 9 5 .
1905.

5.

C h a n d l e r , W. H. F r u i t G row ing. H oughton M i f l i n Co.
The R i v e r s i d e P r e s s .
C a m b r id g e .
1925*

6.

C h r i s t o p h e r , E. P . The I n t e n s i t y o f L i g h t S t r i k i n g
L e a v e s o f A pple T r e e s a t D i f f e r e n t Times o f t h e Day.
P r o c . Amer. S oc. H o r t . S c i . 3 2 : 6 6 .
193^*

7.

Downing, A. J .
F r u i t s a n d F r u i t T r e e s o f A m e r ic a .
Second R e v i s e d Ed. J o h n W iley & S o n s . New Y o rk .
1900.

6.

G a r d n e r , V. R . , B r a d f o r d , F . C . , a n d H o o k e r , H. G.
F u n d a m e n t a l s o f F r u i t P r o d u c t i o n . M c G raw -H ill Book
C o., I n c .
New York.
1922.

9.

G o u r l e y , J . H.
Some E f f e c t s o f S h a d i n g Some H o r t i ­
c u ltu ra l P lan ts.
P r o c . Amer. Soc. H o r t . S c i . 16:
256.
1 930.

10.

H e i n i c k e , A. J .
The D a i l y R a te o f P h o t o s y n t h e s i s ,
d u r i n g t h e Growing S e a s o n o f 1935 >
a Young Apple
T re e o f B e a r i n g Age.
New York A g r. Exp. S t a . ( C o r n e l l )
Mem. 2 0 1 .
1937*

11.

H e i n i c k e , A. J . a n d H offm an, M. B. The R a te o f P h o t o ­
s y n t h e s i s o f Apples u n d er N a tu r a l C o n d i tio n s .
P a r t 1.
New Y o r k A g r . Exp. S t a . ( C o r n e l l ) B u i . 5 7 7 . 1933*

12.

H o o v e r , W. H. , J o h n s t o n , E. S. and B r a c k e t t , F . S.
Carbon D i o x i d e A s s i m i l a t i o n i n a H i g h e r P l a n t .
S m ith­
s o n i a n M i s c . C o l l . 67*3-6* 3.933*

-

31 -

P o p p , H. W. E f f e c t o f L i g h t I n t e n s i t y on Growth o f
S o ybeans an d I t s R e l a t i o n t o t h e A u to —c a t a l y s t Theory
o f G row th. B o t . (Jaz. 6 1 : 306- 3 2 0 . 1926.
14.

R i c k s , G. L. and G a s t o n , H. P. The “T h in Wood" Method
o f P r u n i n g B e a r i n g A pple T r e e s . M ich. A gr. E xp. S t a .
S p ec. B u i . 2 6 5 . 1935.

15«

S c h r a d e r , A. L. and M a r t h , P. 0 .
L ight I n t e n s i t y as a
F a c t o r i n D evelopment o f Apple C o l o r and S i z e .
Proc.
Amer. Soc. H o r t . S c i . 2 9 : 5 5 2 . 1 9 3 1 .

-3 2 -

TABLE I I

R e l a t i o n of l i g h t t o t h e p r o d u c tio n of o r g a n ic m a t t e r
•
Light
; P ro d u c tio n of o rg a n ic m a tte r
( f o o t - c a n d l e - h o u r b ) : (grams p e r Bquare meter p e r hou:
•

0
30
70
60
150
160
195
200
210
520
640
640
900
910
920
1010
1060
1090
1090
1350
1400
1565
2640
2660
2699
2710
2710
2760
2650
2679
3160
3760
3770
Y = 0.2352 +0,1282
Sy = ± 0.367
r = 0.899$

:
:
:
:
:
=
:
:
:
:
;
;
:
:
:
:
:
:
;
:
*

:
:
:
:
:
:
:
:
0.00146 X2

.00
*3$
.10
.02
.15
*65
.65
.68
.40
.90
1.19
I .65
1 • 75
1.24
1*75
1.23
1.19
1.94
2.51
1.69
2.32
2.05
2.3.5
2.74
2.68
2.23
3.**
2.52
2.04
2 .3 8
3.48
3.37

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TABLE VI

A Comparison of the Growth of "Thin11 and ‘'Thick" Branches*
and the Amount of Organic Matter Produced
by Their Leaves
Aver.:
leaf :
area :
(cm2 ):

Grams
Dry Weight

"THIN WOOD"
New wood
Wood 1 t o 3
y e a r s old
F ruit

7/21

8/3

1.37

1.49

.12

:
•

.99
20.25

1.30
23.21

T o tal g ain , dry m atter
"THICK WOOD"
New wood
Wood 1 to 3
y e a rs old
Fruit

In­
crease

P roduction of
dry m a tte r
from 7/21 to
3 /3 /3 6

6.45

5.6 6

.31
2.96

:
:

3-39

:

• 59

480 :

8.75 grams

S20 :

31.^0 grams

:
•
•

6.6 6

25.4-9

8 .S3
30.42

T o ta l gain, dry m atter
♦Average of 10 branches

2.17
M 3

:
:

7.69

:

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F ig u re 2

COMPARISON OF THE SUMMATION CURVES FOR ORGANIC
MATTER PRODUCTION OF "THICK" AND "THIN11
WOOD LEAVES. 1936.
Grams

300

200

100

-1 0 0

50
75
Days from June 3
"thick*1 wood l e a v e s , summation of p r o d u c tio n
Slope = I . 25O
" th i n " wood l e a v e s , summation of pro d u ctio n
Slope = 0 .0 9 7
25

A:
A]_:
B:
Bx :

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le af area per day
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FIGURE

k

COMPARISON BETWEEN THE SUMMATION CURVES FOR DRY
MATTER PRCDUCTION BY "THICK" AND "THIN"
WOOD LEAVES

150

100

Grams

organic

matter

produced

200

g

16

2^

Days from July 13
Slope of line A, 1.3&5
Slope of line B, o *395