THE BOOT GOES IN SEARCH OF FOOD. 93 



the farmer may employ to effect the proper distribution 

 of the nutritive substances stored up in his field, and to 

 make the earthy phosphates, the potash, and the silicic 

 acid available to the roots of the plants, he further im- 

 proves his land by the mechanical operations of agricul- 

 ture, and by removing from the soil all obstacles that 

 hinder the spreading of the roots, as well as those in- 

 jurious agencies which interfere with their normal ac- 

 tivity, or endanger their healthy condition. 



the effect produced by breaking up the ground by 

 the 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 loco- 

 motion of their own, 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 nutri- 

 ment ; 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, arid 

 their outer surface, becoming more woody, is coated in 

 many cases with a layer of corky substance, which, 

 being impenetrable by water, affords, to the soluble 

 matter deposited within, some protection against os- 

 motic influences. 



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

 turnip-roots. It is difficult to understand how this could have been accom- 

 plished otherwise than by an attraction between 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 substance for which 

 they possess a chemical attraction. (Russell.) 



