132 VEGETABLE PHYSIOLOGY 



CHAPTEE IX 



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 in any way approaching that of living substance, 

 have led to a not unnatural idea that they feed upon simple 

 inorganic 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 di- 

 oxide, 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 complexity, which they derive from decaying animal 

 or vegetable matter. We have no reason to suppose that 

 the living substance of these non-chlorophyllaceous plants 

 is so radically different from that of their green relations 

 that it has a totally distinct mode of nutrition. 



