Stkucture and Gkowth. 17 



Roots seem to possess a principle akin to instinct, which 

 guides them in their search for food ; for they invariably extend 

 themselves most rapidly and widely in the du-ection of the 

 richest soil. If a strawberry plant be set in a sandy soil, defi- 

 cient in nutritive matters, and rich earth placed on one side of 

 it, the roots will immediately seek the fertile spot, although at 

 first nowhere in contact with it. A decaying bone or a piece 

 of rotten wood will in the same way be sought out by the 

 roots of a plant requiring the nutritive elements it may contain ; 

 and such objects are often found completely covered by a net- 

 work of minute rootlets. 



The roots of plants have, to a certain extent, the power of 

 selecting their food. In general, they absorb only those sub- 

 stances which are needed to develop and perfect their various 

 parts. Thus, if a pea and a grain of wheat be planted side by 

 side, and made to grow under the same circumstances, the 

 wheat plant will absorb silex (in solution) from the earth, while 

 the pea will absorb none. This power of selection, however, 

 does not enable the roots of plants to reject, under all circum- 

 stances, any deleterious agents which may be brought in con- 

 tact with them; and it is a curious circumstance that sub- 

 stances which are fatal to man are equally so to plants, and in 

 nearly the same way. 



In addition to their principal ofiice, as feeding organs, the 

 roots of plants are believed to be, to some extent, organs o# 

 excretion, throwing off any superfluous or deleterious matter 

 which may have been imbibed either by themselves or by the 

 leaves. They also possess the power of accumulating a store 

 of sap, upon which the plant may draw in time of need. 

 Striking examples of the last-named property are furnished by 

 the turnip, the beet, the carrot, and other plants of the same 

 class. 



In general, roots do not produce buds, and are therefore 

 incapable of multiplying the plant to which they belong ; but 

 to this rule there are many exceptions, some species having 

 the power, under certain circumstances, of forming what are 



