VITAL PROCESSES IN PLANTS 9 



substance, etc., and may be either living or dead. 

 All living cells contain that mysterious and complex 

 substance known as protoplasm, which is the seat of 

 vitality and of all the vital processes, such as growth. 

 The protoplasm of one cell is in communication with 

 that of the cells which surround it. Thus the whole 

 plant is really a mass of protoplasm, divided up into 

 minute compartments by cell walls, through which, 

 however, it is continuous from cell to cell. 



Protoplasm is a very unstable substance. It is 

 constantly in a state of flux, some parts being built 

 up into other substances and others broken down. It 

 is on this fact that vitality depends. 



We have therefore in each cell a machine capable 

 of building up and breaking down, not only substances 

 derived from without, but its own substance. In 

 order that this machinery may work, it requires food 

 —that is, raw material from which to manufacture a 

 finished product. 



Both in animals and plants, the food necessity is 

 ever present, but plants obtain their food in quite a 

 difierent way to animals. Animals can make use of 

 substances of an extremely complex chemical nature, 

 built up chiefly of the elements carbon, hydrogen, 

 oxygen, and nitrogen. 



On the other hand, the plant makes use of relatively 

 simple substances. The food of the green plants is 

 obtained partly from the atmosphere by means of the 

 leaves, and partly from the soil by the roots. Whereas 

 the Higher Animals have the power of locomotion, 



