16 PLAKT LIFE OK THE FA11M. 



Continuous Changes in Plants, In this place we must 

 confine ourselves to the few passing references already 

 made, but one thing we must strive to impress forcibly 

 on the reader, because, if the notion is well grasped, it 

 will enable him to understand plant life so much more 

 vividly. We allude to' the continual changes that are 

 going on throughout the whole living fabric of the plant 

 while in its active condition. Cell membrane, the pro- 

 toplasm, the entire mass of liquid and solid constituents 

 of which the plant consists, are, as we have seen, made 

 up of molecules, each, as it were, with a life of its own, 

 undergoing continual changes according to different cir- 

 cumstances, acting and reacting one upon another, so 

 long as any active life remains. Active life, indeed, is 

 ceaseless change ; dormant life is a condition of equi- 

 librium, more often talked about than realized in fact, 

 it is merely relative it implies merely a lessened degree 

 of activity. From this physical point of view the death 

 of a cell is only a change, a rearrangement of particles, 

 never, however, to be recombined into a new growing 

 cell, as happens in the case of a still living cell in the 

 full tide of growth and activity. 



Nutritive Value of the Substances absorbed by Plants, 



The importance of water may be judged from the fact 

 that while succulent vegetables contain more than ninety 

 per cent of water, timber felled in the driest time seldom 

 contains less than forty per cent (Warington). 



As to the nature of the saline substances, reference 

 must, as has been said, be made to the "Chemistry of 

 the Farm " and other works for full details. Suffice it 

 here to say that certain of them, though always in rela- 

 tively small proportions, are essential to the life of the 

 plant ; certain others, generally met with, though useful, 

 are not indispensable. The former comprise salts of 

 potash, magnesia, lime, iron, and in addition phosphorus 



