Jan. i9,1924 
Photoperiodism and Hydrogen-Ion Concentration 
*33 
diictive structure, and it is interesting to note that the P H value is the same 
as that finally attained in the apex in advanced vegetative development 
4 /‘ here is but little change in acidity in upper and lower portions 
of the stem except that after 
flowering has been initiated the 
former increases somewhat in 
acidity. As compared with the 
action of long days, the effect of 
the 1 o-hour day on the plant dur¬ 
ing the first 3 weeks of growth 
following germination is to in¬ 
crease the acidity of the cell sap, 
except for the above-mentioned 
temporary decrease in acidity 
under the short-day exposure. 
After the acidity relations 
characteristic of the advanced 
stage of vegetative develop¬ 
ment have become established 
Of 
5.0 
5.2 
5.4 
5.6 
5.3 
€.0 
6.2 
6.4 
6.6 
) 
AJ 
^—- 
/ \ 
/ 3 
- 
>■——G-- 
l4SFO*-<* 
-oftS 
Ipr 
jfusjk 
111111*11 
ill II 1.1 1 1 
1-U.l 1 III 1 
1-11111111 
111 1 1 1 1 n 
5 V/VE 
abrupt change from long-day to Fig. 3.—Showing the active-acidity relations in the apex and 
short-day conditions results late ' flow H i °^ cosmos when exposed to 
in decided decrease in acidity 
of the apex by the fifth day, 
but this change is not appar¬ 
ent by the second day after 
the transfer had been made 
me oLCJuj. iu lait-nowering cosm 
the long days of summer (Table II). In contrast with 
the sharp progressive increase in active acidity of the apex 
in this group of plants when exposed to long days there is 
but little change in the active acidity of the base of the 
stem. As a result, advance in vegetative development 
leads to a reversal in relative acidity of the apex and 
basal portion of the stem. 
- -- (fig- 5)- Comparing acidity relations 
under the short-day exposure with those under the long-day exposure, 
it is evident that at the time the flowering condition is attained under the 
former the acidity gra¬ 
dient of the axis is 
the reverse of that 
found in the advanced 
stage of vegetative de¬ 
velopment under the 
latter exposure, but is 
similar to the gradient 
found in the earlier 
stages of growth under 
the long-day exposure. 
As a matter of fact, 
the plants exposed to 
the longer daily illu- 
/* 29 9 /3 Ys - s - 1 * mination period show 
*stf/v£ at. a certain stage 
Fig. 4—Showing the course in active acidity of the apex in late-flower- acidity relations quite 
mg cosmos when exposed to the relatively long days of summer and to qjtrnlar ir\ r*t,oroo 
V°' h ^ Ur ^ ay ’ respectively, from date of germination (Table II). In Similar tO tUOSe CiiaraC- 
?^^ y . plantS of t ri S ex P osu re to a io-hour day promptly teristic of the flowering 
initiates flowering. Under these conditions there is during the early .... 
stage of development a well-defined temporary decrease in active Condition, as shown 
f«„%il COmpa /i5 IO )> prob . abl V indicative of initiation of flower- data r»f Tulir A 
^ h , ere 1S a Progressive increase in acidity, culminating in . r" e aa ^a 01 J Uly 6 
heador fruit Pen booms and finaIIy a decrease in the developing seed m Table II. On the 
, ,, r r . ,, other hand, at the mo¬ 
ment the unfolding of the blossom is completed the acidity relations 
are quite similar to those seen in the advanced stage of vegetative 
development. 
5.0 
5.2 
5.4 
5.6 
5.3 
6.0 
6.2 
6.4 
6.6 
a 
Slow. 
ffDS 
A 
OtVE/3 BG 
- ■ 
jf S/OLO* 
bc//>s 
lE/fGT/fOEE^y 
a 
l 
l 
§ 
/(usV 
-L-l 1 1 1 1 1 1 1 
■11 1 1 ! 1 1 1 1 
in . 
-LL1J.U 11 1 
J.n li 111 i 
