RELATION OF WATER TO THE PROTOPLASM 69 
intimately connected with the presence of water in its 
substance. The importance of the ready access of the 
latter is seen further from other considerations. We have 
incidentally alluded more than once to the fact that the 
liquid concerned in these osmotic currents is not pure 
water only, but should rather be regarded as an extremely 
dilute solution of various salts, &¢. Though the protoplasm 
opposes the passage of anything like a strong solution of 
inorganic salts, it allows very dilute ones to enter the cell, 
much as it does pure water. In this way the slowly diffusing 
stream brings to the protoplasm of each cell the inorganic 
materials which are absorbed from the earth, and enables 
the matters elaborated or formed from them by the proto- 
plasm to pass from cell to cell. The feeding or nutrition of 
the various cells, together with the construction of the sub- 
stances which minister to that nutrition, is thus dependent on 
the transit of fluid about the plant in the way described. The 
access of various gases is similarly made possible, for these 
are dissolved in the liquid stream. The oxygen upon the 
presence of which life depends is thus transported to each 
cell, and the carbon dioxide of respiration is removed from 
the seats of its liberation. 
The condition of turgescence is necessary also for growth, 
and for various movements of different parts, enabling 
them to adapt themselves to varying conditions of their 
environment. Some plants, particularly those which are 
aquatic in habit, and such parts of terrestrial plants as 
contain but little woody tissue, are dependent on the tur- 
gescence of their cells for the rigidity which enables them 
to maintain their position in the medium in which they 
live. The maintenance of the turgid condition of the cells 
is further of the highest importance in enabling the inter- 
change. of water between contiguous cells to take place as 
freely as possible, and without intermission. Flaccid cells 
do not effect such interchange with sufficient readiness. 
Flaccidity of an organ is attended by a partial collapse of the 
tissue, which involves a diminution of the volume of its 
