THE RESERVE MATERIALS OF PLANTS. 



AT first sight the story of the metabolism of the vege- 

 table organism seems to be that of a series of much 

 simpler operations than those of the animal one. The food 

 on which it subsists is presented to it in a very simple form, 

 and the elaboration of the plant's substance from such com- 

 pounds as are offered to it by the atmosphere and by 

 the soil involves such a vast amount of constructive change 

 that we may almost be pardoned for overlooking anything 

 of a different nature. Yet it is equally true that vegetable 

 protoplasm, like animal, is quite incapable of using these 

 simple materials for its own nutrition and increase, in the 

 forms in which we see the plant as a whole taking them in. 

 The constructive changes, which we can trace, lead to the 

 formation of vast numbers of bodies of various degrees of 

 complexity and different organic constitution. But this 

 construction must precede the actual nutrition of the living 

 substance, and the food-stuffs on which the latter really de- 

 pends are at least as complex as the food on which the ani- 

 mal lives. The structure of the vegetable organism favours 

 the absorption of the simplest substances, and that chiefly 

 because it is impossible for the elaborate food-stuffs of animal 

 life to enter it. But these unelaborated materials do not 

 nourish the plant without much expenditure of energy upon 

 them. The essential similarity of the ultimate processes 

 appears evident when we consider such organisms as the 

 group of the Myxomycetes, where an approximation to the 

 conditions of animal life is attended by a similar mode of 

 absorption of food material. 



The metabolism of the plant consists then of two essen- 

 tially different processes. The simpler bodies originally 

 absorbed are worked up at the expense of a great out-put 

 of energy into bodies such as those on which an animal 

 lives, and it is only after such formation that the actual 

 nutrition of the organism can be said to commence. 



The needs of the organism are again very similar. The 



