276 PART IV. CLASSIFICATION. 



unseptate, as in the Phycomycetes, in which case the body re- 

 sembles in structure that of the Siphonaceae among the Green Algae 

 (see p. 250 1. 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 coenocytes (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. 239). 



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

 ductive organs form compact masses of tissue of a somewhat 

 parenchymatous appearance, in which there is no differentiation 

 of tissue-systems, but the superficial layers of hyphae form a kind 

 of tegumentary tissue, termed generally cortex. Considerable 

 differences in the nature of the cell-wall may obtain in different 

 parts of such organs, some walls being soft and mucilaginous, 

 whilst others are relatively hard without, however, ever being lig- 

 nified. In a few Mushrooms (e.g, Lactarius) some of the hyphae 

 form a system of laticiferous tissue, and in others glandular struc- 

 tures occur. 



Except in the simplest forms, the body is generally more or less 

 clearly differentiated into root and shoot. These members can be 

 distinguished partly by their relative position, the root-hyphae 

 growing into the substratum, and the shoot-hyphae into the air ; 

 and partly by the fact that the shoot-hyphse bear the reproductive 

 organs. Some parasitic forms have root-like organs, termed 

 haustoria, which penetrate into the cells of the host ; similar 

 organs occur in some saprophytes, and in others (e.g. crustaceous 

 Lichens) the roots (sometimes called rhizines) consist of bundles of 

 hyphae. There is in no case any differentiation of the shoot into 

 stem and leaf. 



The foregoing account does not apply to the body of the Myxomycetes, 

 which consists of a multinucleate mass of protoplasm, termed a plas- 

 modium, without any cell-wall. It is formed by the cohesion of a 

 number of small, originally independent amoeboid cells, like that of the 

 Hydrodictyacese among the Algae (see p. 253). 



Vegetative propagation is common among the Fungi. The 

 simplest form of it is simple cell-division (e.g. Schizomycetes), or 

 that form of cell-division known as budding or sprouting (gemm- 



