The Cell as.an Individual: = 9 , 
it secretes out of itself. Only those cells are in a living state 
‘which still contain protoplasm; such alone can grow, 
produce new chemical combinations, and, under favourable 
circumstances, give rise to new cells. Cells destitute of 
protoplasm are of service to the plant only by their hard- 
ness, their power of attracting water, and their form, or as 
- protecting envelopes. 
_ Every mass of protoplasm, whether free or enclosed in a cell-wall, 
has a definite external boundary, where a layer of it is distinguished from 
the internal portion by the absence of the imbedded granules, and by 
its consequent greater transparency. This layer, called the prvzmordial 
utricle, is not sharply defined on its inside, but passes gradually into the » 
granular and less dense internal mass ; it is thin, being only very rarely 
of a measurable thickness. The protoplasm which is contained within 
a cell-wall does not generally entirely fill up the cavity, but more often 
occurs as a delicate parietal layer lining the cell-wall on the inside, 
_and surrounding the hollow cavity filled with watery cell-sap. | 
The protoplasm is a compound of different organic substances, 
among which albuminous (nitrogenous) are never absent, and usually 
constitute the bulk of it. It therefore easily coagulates, often merely — 
by the addition of water; and this is especially the case in the cells 
of those plants which do not live in water. It nevertheless contains 
_ abundance of water, and is usually very turgescent ; z.e. it possesses in 
a high degree the power of absorbing water between its most minute 
_ particles, and swelling up in consequence somewhat in the manner of a. 
gum. This power of absorbing water is, however, limited ; as soon as 
it exceeds a certain amount, a watery fluid is exuded in drops in the 
interior of the mass of protoplasm, forming cavities or vaczoles within it. 
The protoplasm can combine with water only slowly-and not in any 
desired proportion ; and, even when most strongly magnified, presents 
the appearance of being separated by sharp outlines from the watery ~ 
fluid which surrounds it, or which fills up the cavities in its interior. 
Water passes easily through a layer of protoplasm ; but the latter offers, 
in the living state, a strong resistance to substances, such as colouring ~ 
matters or salts, dissolved in it, which is generally overcome only by 
_ such injuries as destroy the life of the cell. 
‘Every formation of new cells which can be submitted to observation 
_ begins with a change in the protoplasm, the true body of the cell ; and 
‘this substance is consequently the origin of all new development. It can- 
not therefore be destitute of structure, but must be already organised; . 
