i6 DISEASE IN PLANTS. 



the plant, and there appHed to do work, or stored 

 up for a time in order that it may be used to do 

 work at some future time. 



The accumulation of energy thus ensured is 

 associated with corresponding changes of material 

 substance, and the principal means for bringing 

 this about is recognised in the assimilation of 

 carbon-dioxide photo-synthesis. 



In this process energy enters the chlorophyll- 

 corpuscle in the form of the radiant energy of the 

 sun, it is there directed in the mechanism of the 

 protoplasm, so as to do work on the molecules of 

 water and carbon-dioxide which have also been 

 brought into the machinery ; this it does, breaking 

 asunder their stable structure into unstable bodies, 

 which then re-combine in different ways to form a 

 carbohydrate, such as starch, and this starch is 

 temporarily stored as grains, while oxygen escapes. 



Each starch-grain, therefore, is to be regarded 

 as a packet of matter and of potential energy, as 

 it were, capable of yielding up the latter at any 

 future time, when put under such circumstances 

 that it must do so. Such stores of energy-yielding 

 substance, if I may use the much-abused phrase, 

 form the principal food of the plant or of an 

 animal, if it steps in and takes them and we 

 now see that the process of carbon-dioxide 

 assimilation, as it has perhaps unfortunately been 

 called, is not the same thing as the process of 

 feeding, for the feeding i.e. the nutrition proper 

 of the plant does not begin until the food has 

 been thus obtained. 



