CHAPTER III 



SPECIAL MODES OF NUTRITION 



§ I. Parasites. § 2. Saprophytes. § 3. Mycotrophic Plants. § 4. 

 Bacterial Symbiosis. § 5. Insectivorous Plants. 



From the standpoint of nutrition the plant is fundamentally 

 an independent organism. It synthesises organic com- 

 pounds from inorganic carbon dioxide, water, nitrates 

 and other salts as its raw materials and light as its energy 

 supply. It absorbs the carbon dioxide from the air, the 

 water and salts directly from the soil, and, although this 

 substratum is in part a product of the activity of many 

 organisms, it is none the less true that the plant growing 

 on it is neither immediately nor necessarily dependent on 

 these. A number of flowering plants, however, as well as 

 the great and heterogeneous group of fungi, have departed 

 from this characteristic mode of nutrition ; in one way or 

 other they supplement or replace the supply of inorganic 

 raw materials, by absorbing organic compounds. The 

 species which depart widely from the ordinary mode of 

 nutrition are only a small minority, but the variety of 

 methods employed, the curious structural modifications 

 shown, and the bizarre effects of unusual relations have 

 always drawn to them a large share of attention. We may 

 distinguish five biological groups, though these are sharply 

 delimited neither from each other nor from normal 

 autotrophic plants. 



I Parasites — plants organically united to and more or 

 less dependent on other living plants, the hosts. Lower 

 forms — fungi and bacteria — may be parasitic on animals. 



2. Saprophytes — inhabitants of rich humus soils, on 



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