1907] DOUGLAS—INTUMESCENCES ON POTATO 243 
Pot 24. Three shoots (from a whole potato), 150, 170, 180™™ high, with large 
leaves. 
In five days both plants showed many intumescences scattered over the 
leaves. No. 23 was particularly badly affected. There was a cold spell May 7- 
12, with temperature ranging from 62°-68° F., and a cloudy sky most of the time. 
On May 12 it became bright and warm, with a temperature of 72°F. Intu- 
mescences were then formed in great numbers. 
EXPERIMENT VIII 
Two plants were placed in darkness at the same time, with the 
other conditions similar to those of the preceding experiment. 
Pot 25. Two shoots (from a cut potato), 180™™ with large leaves, and 7o™™ 
with small leaves. 
Pot 26. Three shoots (from a whole potato), 240, 170, 170™™, with large 
leaves. 
In five days no intumescences were formed and the leaves became yellow and 
decayed. 
EXPERIMENT IX 
Two plants were placed under whitewashed glass, with their roots 
kept warm. 
Pot 27. Two shoots (from a cut potato), 150 and 150™™ high, with large 
leaves. 
Pot 28. Two shoots (from a cut potato), 200 and 220™™ high, with large 
leaves, ; 
These were covered with bell jars on May 12, a bright warm day with tem- 
both plants. Plant no. 27, as shown in the photograph (fig. 7), was very heavily 
covered with intumescences, both on leaves and stem. 
EXPERIMENT X 
Two plants were placed in the dark, with their roots kept warm. 
Pot 29. Two shoots (from a whole potato), 170 and 220™™ high, with large 
leaves, 
Pot 30. Two shoots (from a cut potato), 160 and 200™™ high, with large 
leaves. 
No intumescences were formed from May 12 to 15, but the leaves became 
yellow and decayed. 
EXPERIMENT XI 
Two plants were kept with their roots cold by packing the pots in 
ice. 
