$82 REPRODUCTIVE ORGANS OF FUNGI.—AGARICUS. 
In the earlier stages of development the young receptacle 
consists of small, somewhat pear-shaped bodies ( fig. 839, B), 
made up of a dense mass of hyphal tissue continuous with that 
of the mycelium, m. As growth proceeds in these bodies, an 
annular air cavity is formed near the upper part, the roof of 
which forms the under side of the pileus, and, growing rapidly in a 
transverse direction, ultimately becomes covered by a number 
of closely set vertical folds placed in a radiating direction from 
the centre to the margin; these are the lamelle or gills, and 
collectively constitute the hymenium (jig. 6, b), upon whith the 
spores are produced in a manner to be presently described. 
The growth of the cap gradually causes the floor of the cavity, 
Fic. 839. 
Fig. 839. A. Vertical section of the common Mushroom (Agaricus campestyis). 
my. Mycelium. vol. Remains of volva. st, Stipe. an. Annulus. 2. Hy- 
menium with its gills or lamelle, la. p. The pileus.—Bs. m. Mycelium 
of Agaricus, bearing numerous young receptacles in different stages of 
development. After Sachs. 
known as the veil or indusiwm, to give way from the margin, so 
that it comes at last to hang from the stalk in the form of a 
fringe or annulus (figs. 6, ¢, and 839, a, an). 
In some species of Agaricus, as the present, the whole plant 
is entirely enclosed at first in a kind of veil or covering (jig. 6), 
called the volva, which ultimately becomes ruptured, and free 
from the tissue forming the membrane on the upper surface of 
the pileus ; but its remains may be seen at the base of the stalk 
( fig. 839, A, vol). 
If a transverse section of one of the lamelle of a mature 
hymenium be made, it will be seen to consist of cells, greatly 
elongated in the centre, constituting the trama (fig. 840, ft), 
but being smaller and more or less rounded towards the peri- 
phery, where they form what is known as the swb-hymenial layer, 
