1907] DOUGLAS—INTUMESCENCES ON POTATO 245 
EXPERIMENT XV 
Two pots were placed in the dark. 
Pot 43. Two shoots, 200 and 230™™ high, with large leaves. 
Pot 44. Two shoots, 300 and 300™™ high, with small leaves. 
In seven days no intumescences were formed. 
EXPERIMENT XVI 
Two plants’were placed in the shade. 
Pot 45. Three shoots, 200, 180, 160™™ high, with small leaves. 
Pot 46. Two shoots, 200 and 220™™ high, with small leaves and a slender 
stalk. 
In seven days no intumescences were formed. 
EXPERIMENT XVII 
Two plants were placed under whitewashed glass and their roots 
kept warm. 
Pot 47. Two shoots, 240 and 100o™™ high, with small leaves, but having 
flower buds. 
Pot 48. Three shoots, 60, 150, and 200™™ high, with small stalks and leaves. 
In seven days no intumescences had formed. 
That the intumescences did not form at all in this last series of 
experiments affords a suggestion as to their cause in the first set of 
young plants. The high osmotic pressure in the cells of the leaf is 
very probably brought about by the glucose in the leaves, which is 
furnished in great abundance to the young growing parts from the 
starch in the tuber, and is also assimilated in light by the leaves. 
In the case of these last experiments, the shoots which had been sent 
up the third time from the same tubers would thus be poorly supplied 
with glucose and the osmotic tension in the cells would not be so 
great. SoRAUER (20), in a recent paper on the formation of internal 
intumescences on Cereus nycticalis, found a great abundance of glu- 
cose in the affected tissue and considered this to be the osmotically 
active substance which produced abnormal enlargement of the cells 
when a great amount of moisture was supplied. In the tomato 
ATKINSON (1) suggested that this substance is some organic acid, 
the production of which is increased by the low temperature and 
lessened light conditions under which the oedema developed. It is 
therefore very probable that the intumescences in the young potato 
