124 VEGETABLE PHYSIOLOGY 
CHAPTER VIII 
THE FOOD OF PLANTS. INTRODUCTORY 
A good deal of misconception exists as to the nature of the 
food of plants. The character of their environment, and 
the absence in most cases of any means provided in their 
structure for the taking in of any material having a com- 
position at all approaching that of living substance, have 
led to a not unnatural idea that they feed upon simple in- 
organic compounds of comparatively very great simplicity. 
This idea has found considerable support in the fact, which 
is easily ascertained, that such bodies are those which are 
absorbed in the first instance. By their roots when they 
live fastened in the soil, or by their general surface when 
they are inhabitants of water, comparatively simple inor- 
ganic salts are found to enter them with the water which 
they take up. By their green parts, and especially by 
their leaves, carbon dioxide is absorbed, either from air or 
water, according to their habitat. A study of the whole 
vegetable kingdom, however, throws considerable doubt 
upon the theory that these compounds are, in the strict 
sense, to be called their food. Fungal and phanerogamic 
parasites can make no use of such bodies as carbon dioxide, 
but draw elaborated products from the bodies of their 
hosts. Similarly those fungi which are saprophytic can only 
live when supplied with organic compounds of some com- 
plexity, which they derive from decaying animal or vegetable 
matter. We have no reason to suppose that the living sub- 
stance of these non-chlorophyllaceous plants is so radically 
