Jan. X 9 ,1924 
Photoperiodism and Hydrogen-Ion Concentration 
149 
In the preceding experiment the soy beans were not planted till July 
1 and consequently under the natural length of day flowering began 
about 10 days later than the normal date of flowering for earlier plant¬ 
ings. In repeating the experiment, the results of which are shown in 
Table VI (p. 138),plantings were made May 15,and in this case flowering 
began September 4 under the natural length of day. The changes in 
acidity as shown in Table VI are much the same as in the previous ex¬ 
periment, under both the natural length of day and the io-hour day. In 
this instance flowering apparently was initiated about July 27, but, 
because of the greater length of the day as compared with that prevailing 
at the transition period in the preceding experiment, 39 days were re¬ 
quired for the appearance of open blossoms. This is in agreement with 
previous experience (see 8 , p. 882). 
There is no satisfactory evidence that the drop in acidity of the sap 
which occurs during the transition from the vegetative to the flowering 
stage stands in a causal relation to this phenomenon. It seems more 
likely that the sudden decrease in acidity marks a temporary cessation of 
metabolic activity of the type concerned in stem elongation and of which 
the acidity itself is a product. It is to be remembered that light is not 
necessary for the decomposition of organic acids in the plant, while, on 
the other hand, exposure to light does result in the formation of these 
acids. The above results, if they have been correctly interpreted, are of 
interest, however, in indicating the triggerlike character of the transition 
from the vegetative to the flowering condition and furnishing a means of 
recognizing the very early stages in the series of transformations involved. 
It is quite possible, moreover, that these changes in acidity, as a link in 
the chain of events set up, in the first instance, by change in the light 
period, have important end results in influencing plant metabolism. The 
acidity relations in the plants under the io-hour day in comparison with 
those under the natural length of day, as brought out in .figure 10 and 
Tables V and VI, are in full agreement with the observed responses of 
the plants under the two conditions. Similar relationships are seen, also, 
in the data obtained with cosmos, Tithonia, and other species. 
CARBOHYDRATE RELATIONS IN PHOTOPERIODISM 
In view of the attention which plant physiologists have given in recent 
years to carbohydrate content of the plant as a factor in flowering and 
fruiting it seems desirable to include in the present paper the results of 
preliminary observations on the influence of length of day on the con¬ 
centration of soluble carbohydrate in the tissues of the plant. Discus¬ 
sion of the literature on the general subject of carbohydrate content 
in relation to sexual reproduction is deferred till more complete data 
are available on effect of duration of the light period on the carbohydrate 
relations of the plant. In this connection mention should be made of 
recent work by Nightingale ( 21 ) dealing with the effect of the light period 
on the behavior and the chemical composition of certain plants. This 
author suggests that the duration of the light period is a factor in the 
utilization of carbohydrate for the conversion of nitrate nitrogen into 
protein form. In certain varieties of buckwheat, soy beans, radish, and 
salvia a 7-hour day limited the synthesis of nitrates to insoluble forms of 
nitrogen, even though an available supply of carbohydrate was present. 
In tomato plants already containing an abundance of carbohydrates 
shortening the light period caused marked decrease of carbohydrate 
