PLATE 9 
A. —Silversion onion plants from sets which were planted May 19. Plant at extreme 
right is representative of a series exposed to the full seasonal length of day in the open 
air. These plants flowered in July, formed bulbs, and passed through the usual 
summer rest period after the tops had died down. In the series represented by the 
second plant from the right, which were exposed to a 13-hour day, the growth of tops 
was much greater while the bulb was delayed in forming and was reduced in size. 
The plant in center is representative of those exposed to a io-hour day. In this case 
there is no summer rest period and no bulb is formed, the tops remaining green indefi¬ 
nitely. The individual at extreme left shows the behavior of plants grown under 
the natural length of day in the greenhouse, where the temperature was considerably 
higher than out of doors. The behavior was the same as mat of the controls in the 
open except that the size attained was materially reduced. With the addition of 
electric illumination from sunset till midnight in the greenhouse only a slight atten¬ 
uating effect was observed, as shown by the second plant from the left. Photographed 
July 28. (Compare PI. 18, A.) 
B. —Biloxi soybeans, showing partial tuberization of the stems in the vicinity of 
the nodes which results from exposure to a length of day which is too short to admit 
of free flowering and fruiting. Under these conditions flower and fruit are unable 
to fully utilize nutritive material reaching them, and these materials are deposited 
in the surrounding tissues in the more condensed form characteristic of tuberized 
structures. 
