CHAPTER XL 



CHEMICAL PEOCESSES IN THE PLANT. 



I. ASSIMILATION. 



231. In many plants the food materials which are taken 

 into the plant-body are of such a nature that they can be 

 directly used by the protoplasm ; thus in the saprophytes 

 the solutions of organic compounds derived from the decay 

 of animal or vegetable tissues are imbibed by the protoplasm 

 and used by it as true food ; and in the parasites the proto- 

 plasm and the juices of living tissues are directly used in a 

 similar way. It is, furthermore, probable that in some of 

 the lowest forms of vegetation, as in the Myxomycetes and 

 Schizomycetes, the protoplasm is capable of making, to a 

 limited extent, a direct use of some of the inorganic sub- 

 stances absorbed by them. For the most part, however, the 

 principal food materials taken in by plants are such as can- 

 not be directly used by protoplasm in either its vegetative 

 or reproductive activity ; thus neither water nor carbon 

 dioxide is directly used as food by the protoplasm of ordi- 

 nary green plants, but in all cases they undergo certain 

 chemical changes, by which they are made suitable for use 

 by protoplasm. To these preparatory changes, which fit the 

 crude food materials for protoplasmic food, the general name 

 of Assimilation has been given. 



232. It is impossible as yet to give a complete statement 

 of all the processes in assimilation ; the principal facts now 

 made out appear to be as follows : In the chlorophyll- 

 bearing portions of plants, carbon dioxide and water are de- 

 composed, and from their component elements carbohydrates 

 are at once formed. This decomposition and subsequent 

 combination take place only in the granules or masses of 



