127 
Genus Coprimes. 
radiating from the stem-like point ; such Fungi grow hori- 
zontally, and in the most perfect representatives the pileus 
has reversed the position characteristic of the first group, 
and we find the gills occupying the under surface, pointing 
towards the ground. Panus stypticus illustrates this stage 
of development. In type three, illustrated by the species 
of Paxillns , we get shadowed in the umbrella-type of structure, 
so characteristic of the Agaricineae ; the stem has crept within 
the margin of the pileus, at first near to one edge, or ex- 
centric ; in the higher species originating from the centre 
of the under surface, or central ; the gills always run down 
the stem for some distance, thinning out into mere lines, 
and are described as decurrent. In type four, which includes 
the greatest number of species, the stem is always central, 
the gills never decurrent, springing from the stem by their 
entire width — adnate — or more or less cut out behind — 
adnexed — but always touching the stem. In the fifth and 
highest type of structure, the stem is central, and the gills 
are so much cut out behind that they are quite free from 
the stem, as in the genera Pluteus , Amanita , &c. 
From the above it will be seen that there are three leading 
lines of departure from the primitive type of structure : — 
(i) Turning the hymenium downwards, away from the light, 
thus securing protection from sun, rain, &c., until the spores 
are mature: (2) The acquisition of a central stem; the stem 
in itself is an advantage in elevating the pileus from the 
ground, and thus facilitating the dispersion of the spores 
by wind, &c. ; and its central position renders possible the 
closely- set radial arrangement of the gills, a plan which 
secures the greatest possible hymenial or spore-bearing surface 
with the least expenditure of material : (3) The freedom of 
the gills from the stem ; the advantage of this point is not 
obvious, at least not to me, but the persistence with which 
it is carried out in all the highest forms prove it to be of 
some decided advantage. 
Contemporaneously with the above phases of development 
we find the gradual evolution of the protective structures, 
K 2 
