276 DISEASE IN PLANTS. 



are being formed by assimilation, and when, there- 

 fore, no visible permanent enlargement occurs. 

 Similarly, during periods when disintegration of 

 the molecules prevails, we must not assume that 

 the assimilation of new molecules is not occurring 

 and that growth is not proceeding. The two 

 processes are always going on during the active 

 life of the protoplasm : in fact life consists in 

 the play of these processes, as already said. 



That numerous chemical rearrangements of the 

 atom-complexes take place outside the proto- 

 plasmic molecules both of those left unemployed 

 in assimilation and of those rejected during the 

 destructive processes will be readily understood : 

 many of the bye-products found in plants, such 

 as vegetable acids, alkaloids, colouring matters, 

 crystalline bodies, etc., etc., are due to these, 

 so to speak, fortuitous combinations and re-com- 

 binations. 



The part played by respiration has often been 

 misunderstood. It consists in the burning off of 

 some of the carbon and hydrogen of the shattered 

 protoplasm molecules, b)' means of the oxygen of 

 the air, which finds its way into the fluids around 

 the protoplasm, and when it is active every act of 

 combustion which is here an explosion leads 

 to the shattering of more protoplasm molecules, 

 and consequently to more respiratory combustion 

 of the products. If the supply of oxygen is 

 limited the breaking down of the molecules of 

 protoplasm does not cease, but the carbon and 

 hydrogen which would otherwise have been 



