British Gaslromycetes. 9 
bility of commensalism, as already shown by Rees and Fisch 1 
to exist between the species of Elaphomyces and fir-trees. 
The sporophore originates from the mycelium as a minute 
spherical weft of undifferentiated hyphae, in which air-spaces 
are observable at a very early period. Somewhat later the 
gleba or central portion of the weft becomes broken up into a 
large number of irregular sinuous cavities, at first traversed by 
slender hyphae from wall to wall, which eventually disappear. 
The septa separating the cavities undergo further differentia- 
tion into a trama, with the hyphae running more or less 
parallel to the walls, and a hymenium consisting of closely- 
packed terminal cells, originating from the hyphae of the 
trama, arranged perpendicularly to the surface, which in all 
genera, except Melanogaster , forms an even wall lining the 
cavities. In the last-named genus the fertile cells of the 
hymenium are of various lengths, and at first fill the cavities. 
The basidia are clavate except in the genus Hymenogctster , 
where they are generally cylindrical, not thicker than the 
sterile cells, and when fully developed project considerably 
beyond the level of the hymenium ; Tulasne has figured a 
portion of the hymenium of Hymenogaster decorus 2 , where, in 
addition to the normal type of basidia, two slender branches 
of the trama have pushed beyond the hymenial surface, and 
without undergoing the slightest morphological change, each 
supports a perfectly developed spore at its apex. It has 
become the fashion of late to consider spores produced on 
hyphae that do not present the structure characteristic of 
basidia, as gonidia, but in the genus under consideration, as 
indeed throughout the group, great variability is observable 
in the elements of the hymenium, and the distinction between 
so-called gonidia and basidiospores becomes meaningless, and 
only proves the group to represent the starting-point of the 
Gastromycetes. Numerous instances of similar instability in 
the spore-bearing threads of the hymenium are present in such 
genera as Pistillaria , Aleurodiscus , and Corticium amongst the 
1 Uhlworm and Haenlein’s Bibl. Bot, Heft VII. 24 pp. and 1 PI. (188;), 
2 Fungi Hypogaei,-t. x. Fig. IX. 2 . 
