64 VEGETABLE PHYSIOLOGY 



fusing 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. 



The importance of the water supply, and indeed its 

 necessity to the plant, explains the existence of certain 

 subsidiary mechanisms for its absorption and storage 

 which are occasionally met with. These will be considered 

 in detail in a subsequent chapter, but a few of such 

 adaptations may be noticed here. We frequently find 

 particular aggregations of cells set apart for storage of 



