PHTSIOLOGT 



made in 1873 by Pfeffer, in his studies on the 

 movements of irritable plant organs. He in- 

 vestigated particularly the behavior of certain 

 stamens which, when touched by an insect, 

 suddenly shorten, thereby depositing pollen 

 upon the insect. The shortening is due to the 

 giving out of water by the cells of the stamen j 

 the water moves into the intercellular spaces, 

 from which it is reabsorbed by the cells during 

 the subsequent process of recovery. This reab- 

 sorption stretches the cell walls, thereby length- 

 ening the stamen. To accomplish this a consider- 

 able force is required, which Pfeffer estimated 

 at from two to four atmospheres. 



At that time no one could explain how so 

 much pressure was produced. Pfeffer sought to 

 throw light on the question by constructing a 

 model which would act as nearly as possible like 

 the living cell. He prepared an unglazed porce- 

 lain cup in the pores of which he produced a 

 deposit of copper ferrocyanide (after the 

 method of Traube) : this was closed by a stopper 

 in which a manometer was fixed. The membrane 

 of copper ferrocyanide is permeable to water but 



