THE GENEKAL STKUCTUBE 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 vacnole. 



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 special differen- 

 tiated portion called the nucleus. 

 Sometimes, but only in particular 

 cells, the protoplasm contains other 

 differentiated portions, distinct from 



r FIG. 6. ADULT VEGETABLE 



the rest ot the substance, which are CELLS, x 500. (After 

 known as plastids. The bulk of the 



cell-wall ; p, protoplasm ; 

 k k, nucleus, with nu- 

 cleoli ; s s', vacuoles. 



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 



