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CHAPTER IV 
THE RELATION OF WATER TO THE PROTOPLASM OF THE CELL 
WHEN we regard the arrangement of protoplasm in the 
cells of the plant, or observe the environment of the free- 
swimming protoplast, we notice especially its very close 
relation to water. The naked zoospore is naturally 
saturated with the latter, being in the fullest contact with 
it. Unicellular plants which are not actually immersed in 
it are generally to be found in more or less moist situa- 
tions, where they continually obtain supplies from dew or 
rain. Indeed in times of drought when moisture is not 
supplied to them they are seriously injured. The young 
cell which is clothed with a cell-membrane speedily shows 
a tendency to accumulate water in its interior; gradually 
drops appear, which lead ultimately to the formation of a 
vacuole, which is always full of liquid. In a plant which 
consists of a complex of cells, such a vacuole is found in 
every adult cell so long as it is living. The healthy proto- 
plasm is thus always in contact with water. Indeed the 
molecular constitution of protoplasm, as far as we know it, 
lends itself to this relation, for the apparently structureless 
substance is always saturated with it. It is only while in 
such a condition that active life can exist; with very rare 
exceptions, if a cell is once completely dried, even at a low 
temperature, its life is gone, and restoration of water fails 
to enable it to recover. 
The constancy of the occurrence of the vacuole in the 
cells of the vegetable organism is itself very strong evidence 
that such cells are dependent upon water for the main- 
tenance of life. The cell-wall, though usually permeable, 
