Gullliermond - Atkinson 



14 



Cytoplasm 



mic layer, or plasmalemma, in opposition to the rest of the cyto- 

 plasm which is designated as endoplasm. This is the only mem- 

 brane which exists in the Plasmodium of the Myxomycetes, in the 

 Myxamoebae, as well as in various zoospores and spermatozoids 

 of the algae and fungi. In other material, especially in the lower 

 organisms, the equilibrium forms of the protoplasm when in the 

 presence of water consist of lobes or pseudopodia, irregular and 

 changing, blunt or spiny, perhaps in accordance with temporary 

 and local modifications of surface tension. There again everything 

 goes on as if there were an elastic layer around the cytoplasm. 

 Figure 8 represents the division into two tiny plasmodia of 

 Vampyrella. The individuals in the process of separation remain 

 for a long time united by a protoplasmic strand which becomes 

 increasingly thin. Then suddenly it breaks in the middle and the 



Fig. 8. — Division in Vampyrella. ps, pseudopodia. 



two points liberated by the rupture go back into the plasmodia to 

 which they belong as if pulled back in by the contraction of an 

 elastic membrane. In all other cells it is recognized that an anal- 

 ogous membrane lines the cellulose wall. When a plant cell is 

 plasmolyzed, for example an epidermal cell of Iris germanica, the 

 cytoplasm leaves the cellulose wall and contracts in the middle of 

 the cellular cavity to a perfectly delimited spherical mass as if it 

 possessed a delicate external membrane. 



Following work by de Vries on the osmotic phenomena 

 of plant cells, there was often given to the region of demarcation 

 between the cytoplasm and the surrounding environment, the value 

 of a differentiated membrane to which the semi-permeability of the 

 cells has been attributed. In no case, however, can this membrane 

 be detected morphologically by any kind of staining. Therefore 

 its existence as a differentiated membrane is purely theoretical 



