26 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



enlargement takes place after smothering or clogging acids have 

 been broken down and that it ceases when the supply of " building 

 material " is reduced to a minimum. 



8. The action of light on growth has been considered only with 

 reference to its disintegrating effects on acids, and as affecting 

 transpiration and air-temperature. The direct action of light on 

 protoplasts and on body temperatures will be discussed in a later 

 paper. 



Explanation of plate i 



Group of auxographs recording variations in volume of Opuntia discata. A joint of 

 this plant growing as a water culture at the left. Desert Laboratory. 



