PLATE 91 
A. —Plants grown at a soil temperature of 15 0 C. Thirty-eight per cent of the grow¬ 
ing points were destroyed at this temperature. 
B. —Plants grown at a soil temperature of 18 0 . The most severe tissue destruction 
occurred at this temperature. Note that at only two points along the underground 
portion of the stein does the cortex remain uninjured! Of the five steins from this 
tuber, three were “cut oh.” Thirty per cent of the growing points were destroyed. 
