:MAXXER in which roots take up food. 101 



held ill solution by the water moving about in the soil 

 may not, under certain circumstances, be absorbed by the 

 roots of the plants. But it is based upon the assumed 

 fact, that the roots receive their food from the thin layer 

 of water which, retained by capillary attraction, is in 

 intimate contact with the earth and with the root surface, 

 and not from more remote layers of water ; that betw^een 

 the root surface, the layer of water, and the earthy par- 

 ticles, a reciprocal action goes on, wliich does not take 

 place between the water and the earthy particles alone. 

 It also assumes as probable, that the nutritive substances 

 adhering, in a state of exceedingly minute division, to the 

 outer surfiice of the earthy particles, are in direct contact 

 w^ith the fluid of the porous absorbent cell-walls, by means 

 of a very thin layer of water ; and that the solution of 

 the sohd elements is effected in the pores of the cell- 

 walls, whence they pass immediately into the system of 

 the plant. 



The facts in support of tliis view", briefly recapitulated, 

 are as follow : The roots of all land-plants, and of most 

 marsh- plants, are in direct contact Avith the earthy 

 particles. These particles of earth have the powder of 

 attracting the most important elements of food conveyed 

 to them in watery solution (such as potash, phosphoric 

 acid, silicic acid, ammonia), and of retaining them, just as 

 charcoal retains colouring matters. In most cases that 

 have been investigated it has been found that the water 

 moving about in the ground extracts from the soil 

 scarcely any appreciable quantities of ammonia, no phos- 

 phoric acid, and potash in such trifling quantities, that all 

 these together are quite insufficient to afford the requisite 

 supply of these elements to the plants growing in the 

 field. 



Water stagnant in the ground, so far from promoting 



