Response of P!ants_Relative to Length of Day and Night 
Plate 4 
A. —Yellow Cosmos plant, the upper and lower portions of which were placed in light-proof chambers 
on July 11 and received thereafter 10 hours of light daily, while the central portion continued to receive 
the light of the entire summer day. Both top and bottom of the plant responded in characteristic 
manner to the short day and soon flowered, as shown in the photograph. The central portion, on the 
other hand, remained vegetative in response to the long day. Photographed September 11 
B. —Yellow Cosmos plant, the upper portion of which was maintained in total darkness from July 6 
to July 26 and then restored to the full length of day. While the upper portion remained in continuous 
darkness the lower portion was exposed to a 10-hour day. Flower buds were visible in the lower 
portion July 18, and the first blossom opened August 11. The upper portion was badly etiolated by 
the darkening, but soon recovered when restored to light and was showing flower buds by August 20 
and an open blossom on September 7 in response to the supposed transmitted effect of exposure of the 
lower part of the plant to a short day 
