2] 



EFFECT OX STRUCTURE AND FUNCTIONS 



75 



a. Since a protoplasmic mass is bounded by a Him, permit- 

 ling osmosis, it is clear that its characters may be greatly 

 Ltered by varying the degree of concentration of the solution 

 which it lives ; and we have already seen that they are so 

 llerecl. 



When plant cells, with a rigid cell-wall, are put into dense 

 xLutions, the water is drawn from the protoplasmic sac which, 

 mtracting, is torn from the cell- wall. The salt solution pene- 

 trates through the latter, but cannot enter the bounding plasma- 

 film, which continues to contract around the diminishing glob- 

 le of water until only a small ball remains. 



FIG. 8. 1. Young, not more than half-grown, cells from the cortical parenchyma 

 of Cephalaria lencantha. 2. The same cell in a 4% solution of potassium nitrate. 

 3. The same cell in a 6% solution. 4. The same cell in a 10% solution. 1 and 4 

 from nature, 2 and 3 diagrammatic, all in optical longitudinal section, h, cell 

 membrane ; p, lining layer of protoplasm ; k, cell nucleus ; c, chlorophyll bodies : 

 s, cell-sap ; e, salt solution which has penetrated within the cell-membrane. (From 

 SACHS : Pflanzenphysiologie, after DE VBIES.) 



Put into pure water, on the contrary, the protoplasmic sac 

 becomes distended, provided the cell sap contains an appro- 

 priate solution, generally a plant-acid. Thus turgescence is 

 brought about. 



The same effect of varied density upon the structure of pro- 

 toplasm is observable among animals also. Thus, KUHKE 

 ('64, p. 48) and CZERXY ('69, pp. 158, 161) found that Amoeba 

 shrinks into a spherical mass when put into a \% to 2% NaCl 

 solution, and, when returned to fresh water, swells. Also, the 

 character of the pseudopodia of Amoeba and Myxomycetes 

 changes. They become more numerous and attenuated, so that 



