PLATE 49 
1. —Under surface of a cauliflower leaf from the same series as Plate 48 but nine days 
after 15 minutes' exposure to vapor of ammonia, and not from the same plant. Galls 
much larger and epidermis now ruptured in many of them. Most of the intumescences 
are on the under surface, and they occur in clusters. Probably the stomata on the 
upper surface of leaves, being exposed to the sun, close earlier in the day than those 
on the under surface, and those on the under surface undoubtedly close irregularly 
according to the needs of the various areas of the leaf. (For further evidence of this 
see PI. 55.) The leaves became mottled light and dark green soon after exposure, 
but the phenomenon was fugitive—that is, two hours later they appeared to be normal. 
Photographed on September 6, 1916. X 5. 
2. —Same series as figure 1, but at the end of 18 days, and from the upper surface of 
a leaf. Photographed on September 1, 1916. X3. 
