CHAPTER in NUTRITION 
I. THE NATURE OF PLANT FOOD 
Food 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 Penicillium, 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. 
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