INTUMESCENCES . 



131 



cences formed on grape leaves, in greenhouses, make the 

 very definite statement, "We have established the fact by 



of direct experiments that the intumescences are 



means 



atmosph 



* # # 



" The light is the predominating factor." 



* 



<( 



iti 



s 



most brilliant illumin 



directly under the glass of the houses, that the intumes- 

 cences form in quantity. One does not observe them in 

 the same greenhouse on leaves which are in a diffuse light, 

 or in the shade." They explain this apparent action of 

 the light by stating that the oedematous leaves protect 

 themselves like succulent plants by the formation of a false ' 

 palisade tissue " against chloro vaporization and an exces- 

 sive transpiration," wjiich latter is accentuated by the direct 

 action of the sunlight, both because of light and heat radi- 



ation. They recommend preventing the formation of 



intumescences 



g 



Mis 



Botanical Garden during the present season on 

 vines which were covered with these intumescences, fully 



grape 



bear out the observations made 



Viala and Pacottet. 



The intumescences were found only on the leaves immedi- 

 ately under the glass, while all the leaves in the shade were 

 free from them. 



The above quotations seem to leave the question as to 

 what the influence of light on the formation of these intu- 

 mescences is, in a rather indefinite condition, and it is evi- 

 dent that a good deal of careful experimenting will have 

 to be done to determine the exact nature 

 stimulus, should there be such a one. 



Practically all of the explanations made for the produc- 

 tion of intumescences have, as has been shown, been caused 



of the light 



sibly 



intumes 



cences because of chemical stimulation has been referred 

 to but twice so far as known. Sorauer 31 in describing the 





