Jan. 19 , 1924 
Photopenodism and Hydrogen-Ion Concentration 
151 
buds were first seen on August 17 and under the natural length of day 
they were observed on September 21. Samples for analysis, consisting 
of upper sections of the stems 18 inches in length, were collected at 
intervals, the attached leaves being removed and rejected. The samples 
were taken at 1 to 2 p. m. After taking the green weights of the stems, 
these were cut into 2-inch pieces and plunged into boiling alcohol to 
which a small quantity of calcium carbonate had been added. Boiling 
was continued for 15 minutes. Extraction of sugars from the stem 
material was completed with 50 per cent alcohol. Reducing sugar was 
determined before and after inversion. The water content of the sam¬ 
ples was obtained by drying the extracts and residues at ioo° C. and 
deducting the weights from the green weights of the samples. The 
results of the analyses are given in Table XV. There is in these data 
some indication of change in water content of the tissues as a result of 
change in the light period. Apparently a slight decrease in water con¬ 
tent had taken place four days after .the transfer to a io-hour day had 
been made, while 12 days later, after flower buds had appeared, the 
water content had risen to 2 per cent above that of the plants exposed 
to the natural length of day. In this connection it is to be noted that 
this increase in water content occurs at a time when exceedingly rapid 
elongation of the flower stems takes place. 
Table XV .—Water and sugars contained in the upper portion of the stem of late-flowering 
cosmos as affected by transfer August 5 from the natural length of day of summer to 
a io-hour day. 
Date. 
Water content. 
Total reducing 
sugar after inver¬ 
sion. 
Reducing sugar 
before inversion. 
Sucrose. 
Natural 
length 
of day. 
io-hour 
day. 
Natural 
length 
of day. 
io-hour 
day. 
Natural 
length 
of day. 
10 -hour 
day. 
Natural 
length 
of day. 
io-hour 
day. 
August 7. 
August 9. 
August 21 . 
Per cent. 
84.9s 
85.00 
84.89 
Per cent. 
85.18 
84.64 
86.74 
Per cent. 
18.41 
14.02 
16.25 
Per cent. 
21.02 
20.80 
20.75 
Per cent. 
8.15 
6-37 
7*79 
Per cent. 
IO.40 
6.85 
10.79 
Per cent 
9-75 
7.27 
8.04 
Per cent. 
IO.09 
I 3 - 2 S 
9.46 
It is plain that shortening the light period had a prompt and decided 
effect on the content of soluble carbohydrate. Two days after the change 
had been made there had been an increase amounting to 14 per cent of 
total sugars originally present. Thereafter, total sugars remained prac¬ 
tically constant under the io-hour day, although there was considerable 
fluctuation under the longer length of day. It will be observed that 
transfer to the short-day conditions affected the relative percentages of 
monosaccharid and polysaccharid. The increase of carbohydrate 
within the first 48 hours consisted almost entirely of reducing sugar, 
while 2 days later, with the total sugar content remaining constant, there 
was a marked increase in polysaccharid at the expense of the reducing 
sugar originally present. This change in proportion of monosaccharid 
to polysaccharid seems to be temporary, and subsequently the ten¬ 
dency is toward a return to a more nearly equal distribution between 
the two classes of sugars. Further studies are under way to determine 
whether these relationships are characteristic features of the effect, of 
the light period on internal conditions of the plant in association with 
73432—23-3 
