64 VEGETABLE PHYSIOLOGY 
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 protoplasm to pass from cell to cell. The feeding 
or nutrition of the various cells, together with the con- 
struction of the substances 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 
turgescence 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 interchange 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 intercellular spaces, and hence often a serious 
interference with its processes of gaseous interchange, 
particularly respiration. Nor is the protoplasm unaffected 
