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 

 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 vaca- 

 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 



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

 root of Fritillariaimperialig (longitudinal sections, x 560: 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 iOs being dis- 

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

 cleolus ; h membrane. 



