z] THE VARIOUS GROUPS OF PLANTS 43 



group be taken in the wide sense as including also those organisms 

 which cause such diseases as club-root of Cabbages and allied plants 

 and wasting disease of Eel-grass, it has a considerable economic 

 nuisance-value. Otherwise its members, however interesting, can 

 hardly be regarded as doing more than a very minor amount of 

 scavenging. 



Fungi : These are the Mushrooms, Toadstools, Moulds, Rusts, 

 Smuts, Yeasts, etc., and comprise, with the Bacteria, the main 

 ultimate scavengers of the organic world, besides causing many of 

 the worst plant diseases. The Fungi are a large and diverse group 

 of relatively simply organized plants. They are usually composed 

 of branching tubular filaments (' hyphae ', collectively forming the 

 so-called ' mycelium ') and always lack chlorophyll, though occasion- 

 ally they may be green in colour. Some are unicellular, and many 

 others are microscopic though filamentous ; commonly, however, 

 the filaments are sufficiently numerous or massed to be evident to 

 the naked eye — usually as a soft whitish investment. They contain 

 numerous tiny nuclei and may be divided internally by cross-walls 

 (septa), or, alternatively, be non-septate. When reproduction is 

 taking place Fungi may be variously, even very brightly, coloured ; 

 this is especially the case with some of the larger and often highly 

 characteristic fruiting bodies, such as (those of) Toadstools and 

 Puffballs, which can reach a considerable size. Fig. 1 1 shows some 

 of these fruiting bodies and other reproductive structures of Fungi, 

 which exhibit a great diversity of form. In these fruiting bodies the 

 masses of filaments, instead of being soft and cobwebby as in the 

 Moulds, are so closely interwoven as to form a solid or even hard 

 structure of definite organization. 



As they lack photosynthetic pigments and are not, alternatively, 

 chemosynthetic. Fungi have to obtain their food for energy and 

 body-building by living either parasitically (on or in other living 

 organisms) or saprophytically (by the breakdown of dead organic 

 materials). As parasites they are the cause of numerous and often 

 devastating diseases, especially of plants, and as saprophytes they 

 cause widespread decay and effect a large proportion of the breaking 

 down of elaborated materials such as leaf-mould. Without such 

 breakdown and return of the raw materials into circulation, life on 

 earth would be brought ultimately to a virtual standstill, or even 

 cease altogether — hence the vital significance of Fungi and Bacteria 

 as scavengers. Animal characteristics exhibited by Fungi include 



