INTUMESCENCES . 133 



o 



The fact that Sorauer found these oedemas in both 

 sprayed and unsprayed leaves would lead one to suggest 

 that the formation of the oedema in the potato leaves was 

 not always directly connected with the spraying with cop- 

 per salts. 



Krister 1 * 1 12 , discussii 

 expressed the belief that intumescences might be formed 

 as a result of the introduction of nutrient or poisonous 

 substances. He refers to the relationship existing be- 

 tween intumescences and the galls produced on poplar 

 leaves by Harmandia tremulae and H. globuli. He found 

 that the leaves affected with the galls had a tendency to 

 form excessively vigorous intumescences around the base 

 of the galls when placed on the surface of a culture 

 medium. Kiister is not certain whether this excessive 

 development of intumescences is due to the action of the 

 gall forming pcison, or whether it is connected with the 

 unusual concentration of nutritive substances which form 



as a result of the gall formation. 



© 



form 



cences has been noted in several instances in connection 

 with insect galls. Woods 89 in describing changes brought 

 about in the leaves of carnations, as a result of punctures 

 by aphids, says that " the cells of diseased spots were 

 found to be much larger than normal, and thin walled and 

 oedematous." In the early stages of the disease, the 

 chloroplasts were undeveloped or smaller than in the 

 healthy cells, and were colorless or yellow. Other in- 

 stances of the formation of giant cells in insect galls have 

 been reported from time to time 9 ' 13 . 



Summing up our present knowledge of the cause for the 

 formation of giant cells, especially in intumescences, it 

 may be said that these are generally formed because of the 

 presence of excessive moisture and heat in enclosed houses, 

 aided possibly by the action of light, and that they have 







