BIOLOGY OF COLLYBIA VELUTIPES. 155 
in the earliest stages they may be distinguished from the sclerotia 
in sections, by the fact that their hyphe run for the most part 
parallel to one another, while in the sclerotia they are woven 
together in all directions. The upper surface of the young sporo- 
phore is moreover covered with large simple hairs (Pi. 2. fig. 8). 
When from 2 to 3 mm, high, the hyphæ in the upper part 
spread out to form the pileus, and the characteristic “ button " 
shape of the Agaricinex is thus produced. At the same time a 
certain amount of differentiation takes place in the tissues. In 
the stipes the central hyph: are apparently pulled apart and 
form a loose central tissue, while the outer layers are close and 
compact and covered with large pigment-containiug hairs. The 
pileus also is differentiated into a loose medullary portion and à 
closely felted cortical layer, again covered with large, simple, 
pigment-containing hairs. The tissue which ultimately gives 
rise to the hymenial layers may also be distinguished as slender 
parallel hyphe running in a downward direction. Occasionally, 
in specimens of this size or slightly larger, the loose medullary 
portion appears to be broken down at the base of the pileus 
to form a “tunnel,” but this is not really the case. The sub- 
hymenium is formed directly from the hyphz on the free lower 
surface and is never enclosed in a cavity * (Pl.2.fig. 10). The only 
approach to a velum partiale is afforded by the large hairs of the 
recurved margin pointing towards the stipes, though not confluent 
with it. It is interesting to compare this with the usual type of 
formation of the velum partiale, of which Agaricus melleus, Vahlt, 
serves as a good example. Here the rudimentary tissue of the 
hymenial layers is at first freely exposed, but later hyphæ frorn 
the margin of the pileus and from the stipes grow aeross the 
intervening space and form a velum partiale, which for a time 
keeps pace with the growth of the sporophore by intercalary 
growth but is finally ruptured, part of it forming the ring on 
the stipes. In this case the sporophore is primarily gymnocarpic 
and later becomes angiocarpic; but in Collybia velutipes it is 
truly gymnocarpic in the sense of the word as used by Brefeld, 
for its hymenium is never enclosed either by a velum partiale 
or a volva. 
The development of the gills does not offer any essentially 
new points, but it may be noted that the cystidia can be 
* Qf. Hoffmann, in de Bary's Comp. Morph. of Fungi, ete., p. 297. 
t De Bary, ibid. p. 291. 
