152 
Journal of Agricultural Research 
Vol. XXVII, No. 3 
change from the vegetative to the flowering condition induced by the 
light factor. There is no apparent reason for supposing that these 
changes in carbohydrate content are directly connected with photosyn¬ 
thesis, since the increase in soluble carbohydrate is caused by decrease 
in the duration of the illumination period. 
Scarlet Globe radish was planted in the greenhouse September 29, and 
one lot of plants was allowed to grow under the natural length of day 
while a second lot was exposed to an 18-hour day, using electric light to 
prolong the daylight period. On January 10 the two lots of plants were 
sampled for determination of reducing sugar in the sap. Under the short 
day the plants sampled had not developed flowering stems but under the 
long day the plants had developed stems 20-24 inches high and these 
were showing flower buds at the tips. In sampling the thickened root 
only a central horizontal section was used. In the leaf material only the 
stem was used, the lamina being discarded. The stems were divided 
into upper and lower portions, the point of division being somewhat 
below the center. Leaf samples were taken at 10.30 a. m. and the other 
material at 1 p. m. The saps were prepared by grinding and pressing 
the material without freezing and then filtering the expressed juice. The 
results of the analyses are shown in Table XVI. In brief, it seems that 
under the longer light period the content of reducing sugar is consider¬ 
ably greater than under the relatively short light period and the con¬ 
centration in the upper portion of the stem is much greater than in the 
lower. Nightingale (21) also found rapid upward translocation of car¬ 
bohydrate in radish exposed to a long day. Apparently the increase in 
reducing sugar under the longer illumination period is not due simply to 
increased photosynthesis, since under these conditions the thickened 
root undergoes shrinkage as a result of dissolution and translocation of 
storage forms of carbohydrate. 
Table XVI.— Reducing sugar in sap of radish exposed to an 18-hour day and to the 
natural length of day of winter. 
Reducing sugar in 25 cc. of 
sap, calculated as dextrose. 
Material. 
Plants exposed 
Plants exposed 
to an 18 -hour 
to the natura 1 
day. 
length of day. 
Grn. I Gm. 
O.I192 I. 
.0185 j. 
.0332 | 0.0185 
.0292 ; .0193 
Upper portion of primary stem 
Lower portion of primary stem. 
Leaf stem. 
Middle section of tuber. 
CONCLUSIONS 
The phenomena of photoperiodism as presented in this and preceding 
papers emphasize the fact that in addition to influencing the fundamental 
process of photosynthesis—that is, conversion of the chemical elements of 
carbon dioxide and water into carbohydrate—the duration of the daily 
light period may definitely control other parallel processes of funda¬ 
mental importance in plant growth and development. The light period 
may determine not only the quantity of carbohydrate produced but also 
the utilization of this material, and it is not possible to explain either the 
