PLANTS. 



73 



The Power of Selection. A plant has, in a certain sense, 

 the power to make a selection of its food. While any 

 substances dissolved in the moisture of the soil will nat- 

 urally find their way 

 into the plant, only 

 such of these as are 

 needed will be taken 

 up and made use of. 



Both the sap of tim- 

 othy grass, and that of 

 clover, for instance, 

 contain silica. The 

 timothy makes use of 

 this to some extent, 

 but clover, having lit- 

 tle use for silica, per- 

 mits it to remain in 

 the sap. 



It is believed that, 

 in some cases, the 

 roots of plants are 

 able to produce chem- 

 ical changes in some 

 elements of soil, and 

 even of rocks, with 

 which they are brought 



in contact, withdraw- The Essential Partg of a 



ing such parts as are 

 required, and leaving the remainder in the soil. 



Flowers and Seeds. In a general sense, the aim and 

 tendency of plants is finally to produce flowers, and then 

 seeds, which, in their season, are to spring up and pro- 

 duce similar plants, so that the variety may continue 

 perpetually in existence. 



