CHAPTER IX 



THE INFLUENCE OF THE STUDY OF THE NUTRI- 

 TION OF HETEROTROPHIC PLANTS ON THE 

 PROGRESS OF KNOWLEDGE OF THE TRUE 

 NATURE OF THE FOOD OF PLANTS 



IN the previous chapters we have seen how slowly, and 

 with what difficulty, a correct appreciation of the true 

 nature of the food of plants and its assimilation made its 

 way into the minds of botanists. Even now the termino- 

 logy which is frequently employed in speaking of the various 

 nutritive processes tends to obscure their actual nature, 

 for by many writers the term assimilation is applied both 

 to the incorporation of food into the living substance and 

 to the absorption or appropriation of the raw materials 

 from which that food is manufactured prior to its incorpora- 

 tion. At the opening of our period in 1860, the nutritive 

 processes of the plant were held to be antithetical to those 

 of animals ; the plant was considered to be anabolic, build- 

 ing up complex compounds from simple ones, the animal 

 katabolic, breaking them down again. The carbon dioxide 

 absorbed from the air and the mineral compounds taken 

 up from the soil were held to constitute the food of plants, 

 and the constructive changes that follow were thought to 

 correspond to the digestive changes of animals, both being 

 preliminary to actual nutrition. A true conception of the 

 various processes concerned was not reached, indeed was 

 not possible, till the researches of Max Schultze, published 

 in 1861 and 1863, showed that the living substance, or 

 protoplasm, of both animal and plant, is fundamentally 

 the same. As soon as this was realized it became necessary 



