PLATE 2 
A. —Helianthus angustifo litis L. Plants at right were exposed to the full daylight 
period, supplemented with electric light from sunset till midnight, throughout the 
test, which began January 27. Plants at left were similarly treated till September 2, 
when they were given a io-hour daily light exposure. First blossoms appeared on 
these plants October 4. It is seen that the short-day conditions induced very free 
flowering and the response was prompt. Photographed October 15. 
B. —Morning-glory (Ipomoea hederacea Jacq.). Plants from seed which germinated 
June 11. The first blossom on plant at left, exposed to a io-hour day from the outset, 
was open July 10. The first open blossom on plant at right, exposed to the natural 
length of day, appeared September 9. Photographed July 13. 
