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 
