THE ROOT OOES IX REARCII OF FOOD. 85 



the earthy pliosphates, tlie potash, and tlic sihcic acid 

 avaihible to the roots of the plants, he further hnproves 

 his land by the mechanical operations of agriculture, and 

 by removing from the soil all obstacles that hinder the 

 spreading of the roots, as well as those injurious agencies 

 which interfere with their normal activity, or endanger 

 their healthy condition. 



The effect produced by breaking up the ground by 

 plough, spade, hoe, harrow, and roller, depends upon the 

 fact, that the roots of plants go in search of their food ; 

 that the nutritive substances have no locomotion of their 

 OAvn, and cannot of themselves leave the place in which 

 they are. The root, as if it had eyes to see, bends and 

 stretches in the direction of the nutriment ; so that the 

 number, thickness, and direction of its filaments indicate 

 the precise spots where they have obtained food.* 



The young root forces its way, not like a nail driven 

 with a certain force into a plank, but by the addition of 

 successive layers, which increase its mass from within 

 outwards. 



The new substance, which lengthens the extremity of 

 the root, is in contact with the soil. The newer the cells 

 forming at the extremities, the thinner are their walls ; 

 as they grow older, the cell- walls thicken, and their outer 

 surface, becoming more woody, is coated in many cases 



* Pieces of bone are often found completely enclosed by a network 

 of turnip-roots. It is difficult to understand liow this could have been 

 accomplished othei-wise than by an attraction betAveen the spongioles and 

 the substance of the bone. The cells, or their contents, are incessantly 

 attracted by the fresh surface of a substance, for which the contents 

 have a chemical attraction. 



It is owing to this attraction that the roots wind round the piece of 

 bone; they form a root-ball rolled, not from without, but from within, 

 by the new cells constantly formed upon contact with a subsUmce fur 

 which they possess a chemical attraction. (Russell.) 



