58 



GHAPTEE IV 



THE KELATION 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, \vhich 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 



