several distinct types which are sometimes used to limit genera or
sub-genera, since the mode of attachment is usually constant in all
species of a group. The principal relations of the gills to the stem are
described as follows: _Adnate_ when they reach the stem and are set
squarely against it (Fig. 247); _decurrent_ when they run down the stem
(Fig. 244); _sinuate_ or _emarginate_ when they have a notch or vertical
curve at the posterior end (Fig. 246); and _free_ when they are rounded
off without reaching the stem (Fig. 243). In all cases when the lamellae
reach the stem and are only attached by the upper angle they are said to
be _adnexed_. This term is often used in combination with others, as
_sinuate-adnexed_ (Fig. 248, small figure), or _ascending adnexed_ (Fig.
248, larger plant). Sometimes the lamellae are adnate, adnexed, etc., and
have a slight decurrent process or tooth as in _Mycena galericulata_
(Fig. 245). In many plants the gills separate very readily from the stem
when the plants are handled. Sometimes merely the expansion of the
pileus tears them away, so that it is necessary to use great caution,
and often to examine plants in different stages of development to
determine the real condition of the lamellae.

[Illustration: FIGURE 246. FIGURE 247. FIGURE 248.

FIGURE 246.--Tricholoma, gills sinuate, stipe solid.

FIGURE 247.--Panaeolus papilionaceus, gills adnate.

FIGURE 248.--Left-hand small plant, Hygrophorus, gills sinuate, adnexed.
Right-hand plant Panaeolus retirugis, gills ascending adnexed, veil
appendiculate.]

In certain genera the gills have special characteristics which may be
noted here. Usually the edge of the lamellae is _acute_ or sharp like the
blade of a knife, but in _Cantharellus_ and _Trogia_ the edges are very
blunt or obtuse. In extreme forms the lamellae are reduced to mere veins
or ridges. Again, the edge is generally _entire_, i. e., not noticeably
toothed, but in _Lentinus_ it is often toothed or cut in various ways.
In some other plants the edges are _serrulate_, _crenulate_, etc. In
_Schizophyllum alneum_, a small whitish plant very common on dead
sticks, the gills are split lengthwise along the edge with the halves
revolute, i. e., rolled back. In _Coprinus_ the gills and often a large
part of the pileus melt at maturity into a dark, inky fluid.

[Illustration: FIGURE 249.--Section of portion of gill of Marasmius
cohaerens. _t_, trama of gill; _sh_, sub-hymenium; _h