IC)8 FINE-STRUCTURE OF PROTOPLASM II 



fern anulus, seed-coats); they are semi-permeable to sugars. Any 

 substance which has passed the cell wall reaches a second permeabilicy 

 resistance at the cytoplasmic surface. In former times it was assumed 

 that all plasmolytic agents were retained at the plasma surface and there 

 exerted their plasmolyzing action. This led to the paradox that cane 

 sugar, for instance, one of the most important of the nutrients, could 

 not penetrate into the cell. The knowledge, however, that salts like 

 KCNS cause the cytoplasm to swell and bring about cap-plasmolysis 

 of the cell (see Fig. 114) has overthrown rhis assumption and now- 

 adays it is supposed with Hofler (,1934) that the main resistance in 

 plasmolysis should be sought in the vacuole boundary, the so-called 

 tonoplast, instead of in the cytoplasmic surface. This does away with 

 the contradiction inherent in the impHcation that important nutrients 

 do not penetrate into the cytoplasm or, like KNO3, can only do so with 

 great difficulty. 



This penetration into the cytoplasm falls under the concept of 

 intrability. In the case of substances which cause no visible change in 

 the cell, their presence within the cytoplasm cannot always be 

 proved easily. Yet the phenomenon can be very well observed, in the 

 case of vital staining with chrysoidin, which often does not enter the 

 vacuole. On the strength of these experiments it is supposed that the 

 outer boundary layer of the cytoplasm is dilferent in nature from the 

 inner one around the vacuole. 



In the phenomenon of deplasmolysis the plasmolysing agent must grad- 

 ually invade the vacuole also. For this process Hofler wants to reserve 

 the designation permeability. However suitable this distinction may be for 

 botanical objects, in which most permeability studies have been carried out 

 with the aid of deplasmolysis, it is inappropriate for animal cells, which do 

 not possess vacuoles. I do not believe that Hofler's terminology, which 

 we want to apply in this context, would cause confusion, since for cells 

 without vacuoles intrability and permeability are, of course, identical. All 

 the same we are faced with a logical difficulty, for henceforth,by permeability 

 zoologists will understand entrance into the cytoplasm, whereas botanists 

 will understand this as traversing the cytoplasm, i.e. entrance followed by 

 elimination. If this elimination represents a passive diffusion, which is 

 probably the case in deplasmolysis experiments, the difficulty is not fun- 

 damental. In most cases, however, where the elimination occurs in connec- 

 tion with the natural intake of a substance, energy is involved, and the 

 phenomenon should then be considered as active elimination [adenoid activity 

 according to Overton, see CoLLANDERand Holmstrom, 1937). This does 



