BIOLOGY OF COLLYBIA VELUTIPES. 151 
with the normal course of events in other species of Collybia. 
As is well known, several species are in the habit of forming 
sclerotia*, e. g., C. tuberosa, P. Karst., C. cirrhata, P. Karst., C. race- 
mosa, P. Karst.; and at least one species, C. platyphylla, P. Karst.t, 
develops analogous structures in the form of mycelial strands 
which, if hard and dark-coloured, would be termed rhizomorphs, for 
like the latter both sclerotia and strands develop new sporophores. 
In the sporophores of C. velutipes, however, we have a sort of 
delayed sclerotium, capable of acting as such, however, under 
certain circumstances; and thus the greatly reduced condition 
of its sclerotia becomes more intelligible. 
The growth of the lower surface continues for a longer time 
than that of the upper, so that its eonvex surface is gradually 
flattened out, and in some cases where growth is exceptionally 
continued it even becomes concave, and so the gills are far more 
exposed than usual. 
A superficial observation of a growing cluster of sporophores 
at once convinces one that they are responsive to the stimulus of 
gravity, for they contrive to grow so that their gills always point 
directly downwards. This geotropist is easily demonstrated by 
placing a tube containing a growing specimen in a position so that 
the plane of the pileus is at rigbt angles to the ground. In a 
couple of hours the stipes becomes twisted so that the pileus js 
brought into a horizontal position. "l'he process may be repeated 
several times with the same specimen. It often happens that 
sporophores begin to develop on the underside of the block. In 
these cases they invariably wither before complete development 
occurs, unless they are able to curve round it and so attain a 
position where it is possible for the gills to grow downwards. 
The blocks infected in the beginning of February produced 
sporophores eontinually from the beginning of March to the 
middle of June. By this time the majority of them had withered 
however, and were producing secondary sporophores. A further 
crop was formed during the first week in August. 
Cultures grown in the dark or shaded with red blotting-paper 
form an external mycelium iudistinguishable in kind and quantity 
* Cf.Van Tieghem, Bull. de la Soc. bot. de France, t, xxiii, 1896, p. 101. 
t Fayod, Ann. des Sci. Nat. 7 ser. t. ix., 1889, pp. 206, 208, 210; Brefeld, 
Unters. aus d. Gesammtgeb. d. Mykol., H. viii. p. 56. 
1 Fayod, loc. cit. p. 201. Bommer, Mém. Cour. de l'Acad. Roy. Sci. Belg. 
t. liv. p. 14. 
