PHOTOPERIODISM 693 



Momordica Charantia, Soja hispida, and Phaseolus vulgaris maxiiuuni 

 fruiting was obtained with the intermediate Ught period. Maximum 

 relative production of leaf occurred in the long day with Soja, in the very- 

 short day with Phaseolus, in both the long and very short days with 

 Momordica, and was not affected by day length in Benincasa. Relative 

 weight of stem was not much affected by the light period in Momordica 

 and Phaseolus and was greatest with both the long and the very short 

 day lengths in Benincasa and Soja. Relative weight of root in Benincasa, 

 Momordica, and Phaseolus was greatest with the long day, in Hordeum 

 and Sinapis in the intermediate day lengths, and with both the long and 

 very short days in Soja. 



In a study of the relation between top and root size in herbaceous 

 plants Crist and Stout (14) obtained consistently a decided increase in 

 top-root ratio in lettuce and radish with decrease in the daily light period. 

 In a comprehensive investigation of relative development of root and 

 tops in several species representing the long-day, short-day, and indeter- 

 minate types Weaver and Himmel (77) obtained in all cases a close 

 correlation between the transpiring surface and the absorbing system. 

 With a 7-hr. day the growth of both tops and roots was greatly retarded 

 and approximately to the same degree when compared with results in a 

 15-hr. day. In Dahlia, however, there was a greater development of 

 short, thick, tuberous roots in the short day. The available data as a 

 whole indicate that, although there are exceptions, the general tendency 

 with different light periods is toward development of a fibrous root 

 system more or less proportional to the growth of tops. 



In anatomical studies of the stem of tomato and pepper exposed to 

 regulated day lengths Deats (15) found that the amounts of both bast 

 and xylem and the thickness of their cell walls varied directly with the 

 length of day as did also the size of the epidermal cells and amount of 

 cork development. Stems exposed to a short day contained relatively 

 more pith. The height and diameter of the stems and the size and thick- 

 ness of the leaves were directly proportional to the length of day. To 

 study the effect of the light period on fiber production in plants Reding- 

 ton and Priestley (61) grew Aster, Chrysanthemum, Pelargonium, and 

 Polygonum with artificial light, using day lengths of 8 and 16 hr. and 

 continuous illumination. Sclerenchyma was more abundantly devel- 

 oped under the 16-hr. period than with continuous light. With an 

 8-hr. period the thinness of the walls of the fibers was very striking. In 

 cultures of flax, w^heat, and barley exposed to the full day and shortened 

 days of 12 and 9 hr. Doroshenko (17) observed that the moderately 

 shortened day causes reduction in size of the cells and of stomata in the 

 leaves, and an increase in number of stomata and venation per unit of 

 surface area; but with a very short day these effects are reversed. How- 

 ever, the various forms are highly individualistic as to most favorable day 



