THE GENEEAL STEUCTUEE OF PLANTS 5 



with its neighbours on all sides. In such cells the proto- 

 plast when young usually occupies the whole of the interior 

 (fig. 5, A), but when they are adult it generally lies as a 



FIG. 5. VEGETABLE CELLS. 



A, very young ; B, a little older, showing commencing formation of vacuole. 

 p, protoplasm ; n, nucleus ; v, a vacuole. 



peripheral layer round the wall, to which it is closely 

 pressed, while a central vacuole occupies the greater space 

 of the cavity enclosed by the cell-walls (fig. 6). Sometimes 

 the vacuole is crossed by a number of bridles or strands 

 of protoplasm, which generally pass 

 from a somewhat central spot to 

 the periphery. The protoplasm is 

 transparent, but somewhat granular 

 in appearance, and is saturated with 

 water. Somewhere in its substance, 

 whether it fills the cell-cavity or 

 not, there exists a specially differen- 

 tiated portion called the nucleus. 

 Sometimes, but only in particular 

 cells, the protoplasm contains other 

 differentiated portions, distinct from 

 the rest of the substance, which are 

 known as plastids. The bulk of the 

 living substance, to distinguish it 

 from these specialised portions, is 



usually called the cytoplasm. It is not of the same con- 

 sistency throughout, a generally firmer portion lying next to 

 the cell-wall being known as the ectoplasm. A similar firm 



FIG. 6. ADULT VEGETABLE 

 CELLS. x 500. (After 

 Sachs.) 



h, cell- wall ; p, protoplasm ; 

 k Jc, nucleus, with nu- 

 cleoli ; s s', vacuoles. 



