THE PLANT. 35 



put together in the process of growth. Let us there- 

 fore suppose a y.oung wlieat-plaut, for instance, to be 

 in condition to commence independent growth. 



It consists of roots which are located in the soil ; 

 leaves which are spread in the air, and a stem which 

 connects the roots and leaves. This stem contains 

 sap vessels, which may he regarded, for the sake of 

 simplicity, as tubes extending from the ends of the 

 roots to the surfaces of the leaves, thus affording a 

 passage for the sap, and consequently allowing the 

 matters taken up to be distributed throughout the 

 plant. 



It is necessary that the materials of which plants 

 are made should be supplied in certain proportions, 

 at the proper time, and in a suitable condition. For 

 instance, carbon could not be taken up in large 

 quantities by the leaves, unless the roots, at the same 

 time, were receiving from the soil those mineral mat- 

 ters which are necessary to growth. On the other 

 hand, no considerable amount of earthy matter could 

 he appropriated by the roots unless the leaves were 

 obtaining carbon from the air. This same rule holds 

 true with regard to all of the constituents required ; 

 Natm-e seeming to have made it a law that if one 

 of the important ingredients of the plant is absent, 

 the others, though they may be present in sufficient 

 quantities, cannot be used. Thus, if the soil is de- 

 ficient in alkalies, and still has sufficient quantities 

 of all of the other ingredients, the plant cannot take 

 up these ingredients, because alkalies are necessary 

 to its life. 



