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MISSOURI BOTANICAL GARDEN 



and excessive water supply, the light factor has been con- 

 sidered as having varying influence on the formation of 

 intumescences. Sorauer 34 refers to the fact that weak 

 illumination favors the formation of intumescences because 



- 



of its lowering the assimilatory activity of the plants. 

 Atkinson 1 holds a similar view, explaining the higher tur- 



gescence of the leaves because of the reduced transpiration 

 in poorly lighted greenhouses. He furthermore refers to 

 the fact "that the lack of light not only favors the ac- 



cumulation of water, 



# 



but it prevents the plants 



He even goes so far as 



from building up strong tissue." 

 to state that " possibly artificial light might be used to 

 advantage " (pg. 108). Trotter 37 likewise says that semi- 

 darkness favors the development of the intumescences. 

 Kiister 11 , in producing artificial intumescences on poplar 

 leaves, found that intumescences were formed on the 

 leaves which were exposed to intense light, particularly on 

 the sides lying on the water, but that in general intu- 

 mescences were formed both in the dark and in the light. 

 Too strong light according to him, however, stops the 

 formation, possibly on account of the reduced transpira- 

 tion. He concludes by saying: "that the formation of 

 intumescences is due to a specific action of light, I am 

 inclined to doubt; it seems more likely that in the bright 

 light, even in the closed dishes, the upper (actual, and not 

 morphologically upper) surface transpired actively, and 

 that therefore no intumescences were 

 side. 



ed on that 



> 9 



As against the claims that darkness favors the forma- 



intumescences 



of recent 



investigations 



seems to indicate that light is extremely necessary to their 

 formation. Dale 3 finds that white light, or in particular the 

 yellow or red rays, are absolutely essential to the develop- 



ment 



In the dark, or in green or 



.blue light, no intumescences were formed on Hibiscus. 

 Viala and Pacottet 38 , in a description of the intumes- 



