NUTRITION OF HYSTEROPHYTES 89 



obtain their food supplies are quite varied. One-celled 

 plants like yeasts and bacteria absorb the organic sub- 

 stances directly, or often decompose them to the appro- 

 priate form by means of digestive ferments called 

 enzymes, which are organic compounds of complex 

 structure whose exact action is not clearly known. Fungi 

 consist of long filaments of cells which either pass 

 through the substances to be absorbed or send little 

 suckers, called haustoria, into the cell of the host, the 

 latter being often the case with fungi parasitic upon 

 living plants. Among the hysterophytic flowering plants 

 some feed on decayed organic matter in the soil, others, 

 e.g. dodder, send haustoria into living plants, and take 

 organic substances directly from them. Some of the 

 mistletoes which possess chlorophyll take little else than 

 water and mineral salts. Of especial interest are the 

 insectivorous plants which catch and digest insects by 

 means of special structures. The digested insects are 

 the source of their nitrogen for many of these plants that 

 live where nitrogen compounds are lacking in the soil. 

 Some plants have fungous hyphae growing partly within 

 and partly outside of some or all of their roots. Such roots 

 are often of peculiar shape and are known as mycorrhiza. 

 The fungi absorb water and mineral salts from the soil 

 and deliver them to the root from which in turn they 

 take organic foods. Some of these fungi are said to be 

 able to make use of the atmospheric nitrogen as do the 

 bacteria in the root tubercles of the bean family. 



134. All the foregoing processes, e.g. transformation of 

 carbohydrates from one form to another, their trans- 

 portation and storage, their building up into proteins, 

 the transportation and storing away of the latter and 

 their building up into protoplasm, require the expenditure 

 of a considerable amount of energy. This must be 



