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. Flaceidity 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 



