312 MR. G. MURHAY ON THE 
all notice of a true external peridium is absent from the de- 
scription. 
In 1879 Capt. Een brought back from Damara-Land among 
his collections a few specimens of B. congregata, which he divided 
between the British Museum and Kew. They were exhibited at 
the time to the Society by Mr. Thiselton Dyer, who called atten- 
tion to the interest of the specimens. When collected they had 
not reached maturity ; and I venture to think they afford an 
explanation of the mode of growth of this interesting fungus. 
The first point to be noted is the presence on them of a definite 
outer peridium of a beautiful white colour still covering the 
immature individuals round the edge of the mass, but apparently 
in the course of peeling off (figs. 1 and 2). It is joined to the 
stroma round the margin, and reaches from it over the tops of 
the inner peridia towards the centre of the group. Each indivi- 
dual is not completely invested by it at all points, but it 
extends over the tops as one continuous membrane common to 
the whole mass, fitting into the depressions between the inner 
peridia, and, in the case of nearly mature individuals, easily 
separable from them. On very young individuals, at the margin 
it is closely united with the inner peridium ; but examination 
with the microscope shows a line of weakness between them, 
destined to become the line of separation. In these cases it 
penetrates downwards between the very young inner peridia, and 
meets the lip of the cup-shaped depression in the stroma in 
which each individual is seated. Directly over the top of the 
mature individuals, in the middle of the mass, it will be found that 
the outer peridium has disappeared. The direction of growth of 
the mass is therefore, I take it, centrifugal. The individuals in 
the centre first become ripe; and in each case, by the expansion 
of the inner peridium, the part of the outer one directly above it 
peels off to permit the discharge of the spores from the beau- 
tifully fimbriated orifice at the apex of the inner peridium. In 
the mean time voung individuals arise round the margin, and 
remain under the covering of the outer peridium until they, too, 
attain maturity and burst it off. When the whole are mature 
(fig. 5), as in the specimens hitherto brought to this country, the 
outer peridium has already disappeared and left no trace of its 
existence behind. 
The microscopic structure of the outer peridium calls for no 
special description. It consists of a mass of very densely inter- 
