32 



THE CELL 



another, and in addition they unite together on the surface to form 

 a continuous layer (primordial utricle), which adheres closely to 

 the inner surface of the enlarged and thickened cellulose 

 membrane. 



Two different conditions which are found in the fully grown 



^ plant cell are the 



B 



Fig. 12. Parenchyma cells from the cortical layer of the 

 root of Fritilloriaimyierialis (longitudinal sections, x 550: 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 ia 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; kk nu- 

 cleolus ; h membrane. 



result of this 

 arrangement. 

 Through the fur- 

 ther increase of 

 the cell-sap, the 

 vacuoles are en- 

 larged, and the 

 partition wall at- 

 tenuated. Finally 

 the latter par- 

 tially breaks 

 down, so that the 

 separate spaces 

 are connected by 

 openings, and 

 thus form one 

 continuous vacu- 

 ole. Consequent- 

 ly part of the 

 protoplasmic sub- 

 stance becomes 

 transformed into 

 a fairly thin layer 

 lying close to the 

 cellulose mem- 

 brane, and the 

 rest into more or 

 less numerous 

 strands and 

 threads travers- 

 ing: the large con- 

 tinuous vacuole 

 which is filled 

 with fluid (Fig. 

 12, right side, and 



