22 DIVISION I.—GENERAL MORPHOLOGY. 
membranes, which our present knowledge enables us to add to what has been already 
said, is that they only occur in Fungi with septate hyphae; the structure of the 
mycelium varies of course in particular points in each species. 
Special generic and specific names have in former times been repeatedly given 
to mycelial membranes which are only known in the sterile state. Persoon’s genus 
Mycoderma! may be composed to a great extent of forms of this kind which belong 
to the Hyphomycetes or to the Ascomycetes. Racodium cellare of Persoon? which 
forms the well-known olive-brown coating on old casks in cellars is, as far as we 
know, a mycelium formed of loosely interwoven filaments, the origin and reproductive 
organs of which are still quite unknown. 
The mycelial membranes named by Tode and Persoon Athelia and Xylostroma 
are of a firmer kind. The Athelieae are the sterile states of the Thelephoreae 
(Thelephora, Hypochnus), in part perhaps their undeveloped sporophores ; the Xylo- 
stromeae, which occur as broad flat formations of a woody or leathery texture in the 
decaying stems of trees, are the like states of firm wood-destroying Hymenomycetes, 
such as Polyporus abietinus, Thelephora hirsuta, Th. crocea, Schrad., Th. setigera, 
Fr., Th. suaveolens, Trametes Pini, Daedalea quercina, and other species of these and 
allied genera. - 
Section VII. The hyphae of the mycelia of many Fungi unite together into 
strands, which in their form, branching, and mode of spreading in the substratum 
look to the unassisted eye more or less like the roots of higher plants. Even 
some species of Hyphomycetes, those for instance known as Acrostalagmus, show 
a tendency to this kind of formation. But it is most frequent among the Fungi 
which have compound sporophores, such as the Phalloideae, many Lycoperdaceae, 
the Hymenogastreae, Nidularieae, and Sphaerobolus, in many of the Agaricineae, 
as A. campestris, A. praecox, A. dryophilus, A. aeruginosus, A. metatus, A. andro- 
saceus, A. Rotula, A. platyphyllus and A. melleus, and amongst Ascomycetes, such 
as Elaphomyces, some species of Genea, Peziza Rapulum, Bull., and P. fulgens; 
the endophytic mycelium of Polystigma stellare, Lk., may. be added to the list. It is 
evident from these examples that the formation of strands is not necessarily found in 
all the species that belong to the cycles of affinity indicated by the above names; on 
the contrary it may be wanting in one of two nearly allied species and be found in the 
other. 
The strands, as has been said, spread themselves out in and on the substratum, 
growing at the apex and putting out similar branches, the arrangement of which 
scarcely follows any exact rule even in the same species. In each case the strands 
may either be in part free and tapering, or they may in part unite to form a coarser 
or finer net-work, or they may in part lose themselves in a loose filamentous web, or 
a single strand or several combined may expand into membranes, which spread 
over the substratum or spin ‘themselves round bodies contained in it. Fresh 
strands may then take their rise from these expansions. This variation of form is 
essentially dependent on the character of the environment and its influence on 
the nutriticn of the Fungus, as is well shown in the case of Agaricus melleus to be 
hereafter described. 
In most cases which have been examined the strands are composed of uniform 

1 Mycol. Europ. p. 96. * Syn. Fungor. 701. 
