312 EDITH BELLAMY SHREYE 



the movements. Quite possibly the movements are either caused 

 by, or controlled by metabolic changes which in their turn are 

 controlled by light and temperature. It is also possible that there 

 are still other intermediate factors. One that forces itself upon 

 the attention is the turgor changes in the tissues. At first it 

 seems absurd that these plant movements could be due to such 

 changes, since the time of lowest turgor would have to come at 

 night, a time when all plants so far as known from previous work, 

 have their greatest turgor. However, it must be noted that 

 all of the changes in environment which have been considered 

 have unavoidably included changes in the evaporative intensity 

 of the air, and therefore in the amount of water lost by trans- 

 piration. Always though, the downward movement occurred 

 when the plant was "logically" losing the least amount of water 

 and an upward one when transpiration was greatest; so that it 

 seems impossible that the plant could have the greatest turgor 

 when the joints are moving upward. 



( To be continued) 



