THK VITAL PROPERTIES OF THE CELL 



155 



The cell sap, 

 however, is not 

 pure water, but 

 a very complex, 

 nutrient solution 

 containing veget- 

 able acids and 

 their salts, nit- 

 rates and phos- 

 phates, sugar, and 

 small quantities 

 of dissolved pro- 

 teids, etc. Thus 

 between the pro- 

 toplasm and the 

 sap material is 

 interchanged to 

 a considerable ex- 

 tent, substances 

 for use being ex- 

 tracted from the 

 one, which in 

 return receives 

 other substances 

 in exchange. 

 Since the sap re- 

 presents a con- 

 centrated solu- 

 tion of osmotic 

 substances, it ex- 

 erts a powerful 

 attraction upon 

 water, and also 

 an internal pres- 

 sure, which is of- 

 ten considerable, 

 upon the envelope 



surrounding it, thus producing a tense condition, which was 

 described on p. 141 as turgor. 



Many botanists, especially de Vries (V. 35) and Went, consider 

 the vacuoles to be special cell organs, which are not of accidental 



FIG. 62, Parenchyma cells from the cortical layer of the 

 root of Fritillaria imperialis (longitudinal sections, x 660 : after 

 Sachs II. 33, Fig. 75): A very young cells, as yet without 

 cell-sap, from close to the apex of the root; B cells of the same 

 description, about 2 mm. above the apex of the root ; the cell- 

 sap (o) forms in the protoplasm (p) separate drops between 

 which are partition walls of protoplasm ; C cells of the same 

 description, about 7-8 mm. above the apex ; the two lower 

 cells on the right hand side are seen in a front view ; the 

 large cell on the left hand side is seen in optical section ; the 

 upper right hand cell is opened by the section ; the nucleus (xy) 

 has a peculiar appearance, in consequence of its being dis- 

 tended, owing to the absorption of water ; fc nucleus ; fcfc nu- 

 cleolus; Ji membrane. 



