PLATE 7 
A. —Tubers of Jerusalem artichoke. The mother plants were grown from tubers 
which germinated April 25 and were exposed to a 10-hour day from the outset. Al¬ 
though flower buds were formed, they were unable to open. By August 15 the tops 
of the plants were dead. Tuberization of the underground stems was complete, 
that is, there was no elongation of unthickened stems. Note the numerous unusually 
prominent buds on the tubers. Apparently the downward translocation of nutrient 
materials was so marked as to cut off the requisite food supply of the flower buds. 
Photographed October 1. 
B. —Tubers from control planting of artichoke exposed to the full seasonal length 
of day. These plants began flowering September 22 and were in full bloom October 1. 
The difference in tuber formation between these plants and those under a io-hour 
day is striking. It is readily seen that under the longer daily light period there was 
marked elongation of the underground stems and only partial tuberization. The 
number of new uiiits formed was greater than under the io-hour day, but they were 
much smaller in size and showed only inconspicuous buds. In this case the activities 
of the plant approach more nearly an even distribution between sexual reproduc¬ 
tion and tuber formation. Photographed October 1. 
