CHAPTER III — NUTRITION 

 I. THE NATURE OF PLANT FOOD 



Fool in general is organic. — The question, what is food for plants, 

 elicits very different answers according to the point of view. The term 

 food is not one which admits of accurate definition, and the difficulty 

 increases the wider the range of organisms to which it refers. A lion 

 obviously lives upon flesh, and the general constituents of his food can be 

 determined. A sheep feeds on herbage, and that can be analyzed. A 

 man consumes meat and vegetables of the most varied sorts. A fungus 

 like PenicUlium, which will grow on a glass of jelly or an orange or a piece 

 of cheese or a plate of gelatin, obviously feeds upon vegetable or animal 

 substances indifferently. The nutritive constituents of flesh and vege- 

 tables are many and diverse; plainly the term which is to include them 

 must be most general. That term by common consent is food. It 

 represents the totality of substances which nourish an organism and 

 enable it to pass successively through the phases of its normal develop- 

 ment. Now all the substances referred to belong to a category known 

 as organic, because they are all produced by the chemical processes in a 

 living organism. Food, therefore, for the lion, the sheep, the man, the 

 mold, is composed of organic substances. It is true that there are also, 

 in the very organic substances themselves and dissolved in the juices 

 which make part of them, mineral salts of various kinds, and that these 

 are indispensable to living beings; but their amount is very small in- 

 deed, and alone they are quite incapable of sustaining life. For the 

 present, therefore, they may be left out of account. 



Is the food of green plants inorganic ? — The beings enumerated 

 represent all sorts of organisms except the green plant. When we ask, 

 "On what does the green plant feed?" the answer, based on analogy, 

 has been, "On the substances that enter it — water, mineral salts, and 

 carbon dioxid; for with these alone it can develop from embryo to 

 maturity." These are inorganic substances; and if the answer be true, 

 the food of green plants is inorganic and that of all other beings organic. 



356 



