[Vol. 2 



564 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



hours or so, and then in most cases there is a decline in the 

 conductivity curve to a point approaching the original posi- 

 tion, after which there may or may not be a gradual incline, 

 depending, probably, on various factors. 



It might be well briefly to consider some theoretical aspects 

 of the subject, especially in regard to the causal agencies ef- 

 fecting the increased exosmosis of the treated cultures. The 

 mere transfer of a culture from a full nutrient solution to dis- 

 tilled water is not in itself sufficient to account for the effects 

 produced, as we have seen that osmotic effects play little or no 

 role in this connection, a conclusion in harmony with the find- 

 ings of Loeb ('03) and of True ('14). To what then is the 

 exosmosis due? Can it all be laid at the door of cell cytolysis? 

 What influence has an alteration of the plasma membrane? 



In any case, we are dealing with the effect of physical and 

 chemical factors upon the plant cell. For our purpose here it 

 is not considered necessary to enter upon a discussion of the 

 various ideas regarding the details of the structure of the 

 cell and its limiting membrane, or the work and theories of the 

 different investigators on both the animal and plant side con- 

 cerning the permeability of the plasma membrane. Yet in 

 passing, it may be well to mention Overton's theory regard- 

 ing the lipoid nature of the plasma membrane, Nathansohn's 

 idea of a mosaic structure of the same, Czapek's experiments 

 indicating the presence of neutral fats in the membrane, Lep- 

 eschkin's view that the plasma membrane is a continuous film 

 (some of the work of the last two investigators being sum- 

 marized by Blackman, '12), and Kite's work on the structure 

 of protoplasm, and also make note of the recent work of Cran- 



ner ( '14) on the lipoid content of the cell wall. 



The effect of the two physical factors, heat and cold, may 

 undoubtedly be considered as resulting in a complete or in- 

 cipient disorganization of the cell, depending upon the dura- 

 tion of exposure, and a consequent escape of some of the con- 

 tents into the surrounding medium. 



In the case of the various chemical factors or agents used 

 the matter is probably not so simple or so easily disposed of. 

 However, a conception that would fulfill the requirements 



