

INTUMESCENCES. 129 



CAUSE FOR FORMATION 



As to the factors which determine the formation of the 

 intumescences there have been various explanations made 

 from time to time. First among these is the explanation 

 which Sorauer made, when he described these structures, 

 and which he has seen no reason to change in later years. 

 He states 26,28 , " Intumescences are formed when the plants, 

 which for some reason have a reduced assimilatory activity, 

 are brought into conditions which bring about an abnormal 

 tumescence in the cells.' ' "I have therefore regarded 

 the intumescences as a symptom of a disturbance which is 



assimi 



lation." 



Sorauer 34 : "S 



be concluded from my knowledge of the vegetative condi- 

 tions operative at the time of the formation of these 

 intumescences, all cases point to the conclusion that the 

 affected plants suffered a stimulus because of a heightened 

 temperature, combined with an excess water supply in the 

 tissues, at a time when their assimilatory activity was 

 depressed because of weak illumination, and that as a result 

 of this stimulus, a reaction took place in the form of a 

 stretching of the cell walls at the expense of the cell con- 

 tents." * * * " Since I have succeeded at other 

 times in producing intumescences experimentally in two 

 cases {Ficus elastica and Impatient fulva) , one must now 

 without question regard these formations as a symptom of 

 an abnormal elevation of temperature and excessive water 



supply." 



Prillieux 20 , Noack 16 , Atkinson 1 , Trotter 37 , and others in 



general hold with Sorauer that high temperatures com- 

 bined with a humid atmosphere and abundant water sup- 

 ply are largely responsible for the formation of intumes-' 



cences. 



In addition to the abnormal elevation of temperature; 



9 



