84 BOTANY. 



to those which absorb the solutions from the soil absorb 

 from the latter, those next removed now absorb from those 

 newly supplied, and so on, from cell to cell, to those at the 

 upper extr-^mity of the plant. In this way, by simple ab- 

 sorption from cell to cell, water and solutions are trans- 

 ported to all portions of the plant-body. Now, many of the 

 cells above ground are often in contact with dry air, into 

 which some of their water evaporates. The cells which 

 suffer this loss of water repair it by absorbing water from 

 contiguous cells, and these absorb from still others, p,nd so 

 on. There is thus a general upward movement of water in 

 the moss-stem due to the loss of water from the leaves. 

 Again, it is seen that the carbohydrates are formed in the 

 green cells alone, and from these they are diffused and ab- 

 sorbed as solutions from cell to cell throughout the plant. 

 Thus there may be an upward movement of water while 

 there is 'a downward diffusion of carbohydrates (and probably 

 of other assimilated matters also). 



154. Nutrition of Higher Plants. — In a plant with a 

 still more complex structure, as, for example, the common 

 sunflower, the cells of the surface of the roots absorb 

 watery solutions, which are then absorbed from cell to cell 

 in the large and numerous roots, finally passing in the 

 same way, from cell to cell in the stem, and even to the 

 leaves and flowers. The loss of water by evaporation from 

 the leaves is much less, proportionately, than from the leaves 

 of mosses, the latter consisting of but a single layer of 

 unprotected cells ; while the active cells in the sunflower- 

 leaf are protected by a layer of specially modified thick- 

 walled cells (the epidermis) less pervious to moisture. 

 When, however, the stomata (breathing pores) are open 

 for the ingress and egress of gases^ much moisture escapes, 



