THE GENERAL STRUCTURE 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, 4), but when they are adult it generally lies as a 
Fic. 5.—VEGETABLE CELLS. 
A, very young; B, a little older, showing commencing formation of vacuole. 
Pp, protoplasm ; 7, 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 special differen- 
tiated portion called the nucleus. 
Sometimes, but only in particular 
cells, the protoplasm contains other 
differentiated portions, distinct from 
. Fie. 6,—ADULT VEGETABLE 
the rest of the substance, which are = Cetts. x 500." (After 
known as plastids. The bulk of the , nee ; 
‘ é : , cell-wall; p, protoplasm ; 
living substance, to distinguish it 4% 4&, nucleus, with nu- 
from these specialised portions, is ieee ogee 
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 
