GROUP 1. THALLOPHYTA : FUNGI. 273 



CLASS H. FUNGI. 



This class, like the preceding, includes many very simple 

 organisms, as well as others of tolerably high development. 

 None of them contain chlpEOphyJl ; hence they cannot assimilate 

 so simple a carbon- compound as carbon dioxide, but must take 

 up their carbonaceous food in the form of rather complex com- 

 pounds, and their structure and mode of life are correlated 

 with this peculiarity. Some are parasitic, such as the Rusts 

 and Smuts, and absorb these complex carbon-compounds from 

 other living organisms, whether plants or animals. Others are 

 saprophytes, absorbing these compounds from the remains of 

 ^KcTorganisms, or from organic substance formed by living or- 

 ganisms : the numerous and often large Fungi which grow on 

 humus or leaf-soil in forests, or on the bark of trees, are examples 

 of the former case ; the Yeasts and Moulds which make their 

 appearance on juicy fruits, saccharine liquids, etc., are examples of 

 the latter. Some Fungi are symbiotic-, that is, they live in inti- 

 mate relation (symbiosis) with plants which possess chlorophyll, 

 and obtain from them the necessary carbonaceous food, but without 

 destroying, or apparently injuring them. They commonly live 

 with Algae, forming Lichens (see p. 319) ; or in connexion with the 

 roots of trees (esp. Cupuliferae) and of Orchids, Leguminosae, and 

 other plants, or with prothallia (e.g. Lycopodium), forming what 

 is known as Mycorhiza. 



The vegetative body may be unicellular, or ccenocytic. In the 

 former case it is small and roundecT or rod-shaped in form. In 

 the latter case the body is always a mycelium, consisting of more 

 or less branched filaments, termed hyphce. The mycelium may be 

 nnseptate, as in the Phycomycetes^in which case the body re- 

 sembles in structure that of the Siphonaceae among the Green Algae 

 (see p. 238). Or the mycelium may be septate, as in the higher 

 Fungi, in which case it appears to be always incompletely septate ; 

 that is to say, the segments of the hyphae which are marked out by 

 the transverse septa, are not cells, each with a nucleus, but contain 

 several nuclei, and are ccenocytes (as in the Cladophoraceae among 

 the Chlorophyceae). The hyphae grow in length at the apex in 

 the manner of such Algae as Vaucheria and Cladophora (see 

 p. 222). 



In some of the more complex forms, the hyphae of the repro- 

 v. s. B. T 



