| 
i 
! 
t 
1907] DOUGLAS—INI UMESCENCES ON POTATO 237 
Intumescences have been observed on various plants by several 
writers, and all practically agree that they are formed under condi- 
tions of excessive humidity accompanied by great warmth. As to 
LA L AAA 
OZ QS I Oo: 
aL te 
@. 
OTS 
Fic. 8.—Old intumescence; parts of the cells have broken away and the walls 
have become cutinized. 
the presence or absence of a light stimulus, there is a greater differ- 
ence of opinion. SoRAUER (10-20), who has described the majority 
Fic. 9.—Large intumescence or patch formed by the union of several intumescences. 
of cases, regards the lack of sufficient light to carry on rapid metabo- 
lism as an important factor in their formation. In “ Die symptomische 
Bedeutung der Intumescenzen” (12), in which a number of cases 
