20 FUNGI. 
the stem, gives the best notion of the arrangement of the 
parts, and their relation to the whole. By this means it will be 
seen that the pileus is continuous with the stem, that the sub- 
stance of the pileus descends into the gills, and that relatively 
the substance of the stem is more fibrous than that of the pileus. 
In the common mushroom the ring is very distinct surrounding 
the stem, a little above the middle, like a collar. In some 
Agarics the ring is very fugacious, or absent altogether. The 
form of the gills, their mode of attachment to the stem, their 
colour, and more especially the colour of the spores, are all very 
important features to be attended to in the discrimination of 
species, since they vary in different specics. The whole 
substance of the Agaric is cellular. A longitudinal slice from 
the stem will exhibit under the microscope delicate tubular 
cells, the general direction of which is lengthwise, with lateral 
branches, the whole interlacing so intimately that it is diffi- 
cult to trace any individual thread very far in its course. It 
will be evident that the structure is less compact as it approaches 
the céntre of the stem, which in many species is hollow. The 
kymenium is the spore-bearing surface, which is exposed or naked, 
and spread over the gills. These plates are covered on all sides 
with a delicate membrane, upon which the reproductive organs 
are developed. If it were possible to remove this membrane in 
one entire piece and spread it out flat, it would cover an 
immense surface, as compared with the size of the pilcus, for it 
is plaited or folded like a lady’s fan over the whole of the gill- 
plates, or lamella, of the fungus.* If the stem of a mushroom 
be cut off close to the gills, and the cap laid upon a sheet of 
paper, with the gills downwards, and left there for a few hours, 
when removed a number of dark radiating lines will be deposited 
upon the paper, each line corresponding with the interstices 
between one pair of gills. These lines are made up of spores 
which have fallen from the hymenium, and, if placed under the 
microscope, their character will at once be made evident. If 
a fragment of the hymenium be also submitted to a similar 
examination, it will be found that the whole surface is studded 
* In Paxillus involutus the hymenium may be readily torn off and unfolded. 
