present more noteworthy features than
others, and will consequently seem to receive more than their
proportional share of attention, but this seeming inequality could
scarcely have been avoided, inasmuch as hitherto some groups have been
more closely investigated than others, are more intimately associated
with other questions, or are more readily and satisfactorily examined
under different aspects of their life-history.

[Illustration: FIG. 1.--Agaric in Process of Growth.]

AGARICINI.--For the structure that prevails in the order to which the
mushroom belongs, an examination of that species will be almost
sufficient. Here we shall at once recognize three distinct parts
requiring elucidation, viz. the rooting slender fibres that traverse
the soil, and termed the _mycelium_, or spawn, the stem and cap or
pileus, which together constitute what is called the _hymenophore_,
and the plates or gills on the under surface of the cap, which bear
the _hymenium_. The earliest condition in which the mushroom can be
recognized as a vegetable entity is in that of the "spawn" or
mycelium, which is essentially an agglomeration of vegetating spores.
Its normal form is that of branched, slender, entangled, anastomosing,
hyaline threads. At certain privileged points of the mycelium, the
threads seem to be aggregated, and become centres of vertical
extension. At first only a small nearly globose budding, like a grain
of mustard seed, is visible, but this afterwards increases rapidly,
and other similar buddings or swellings appear at the base.[A] These
are the young hymenophore. As it pushes through the soil, it
gradually loses its globose form, becomes more or less elongated, and
in this condition a longitudinal section shows the position of the
future gills in a pair of opposite crescent-shaped darker-coloured
spots near the apex. The dermal membrane, or outer skin, seems to be
continuous over the stem and the globose head. At present, there is no
external evidence of an expanded pileus and gills; a longitudinal
section at this stage shows that the gills are being developed, that
the pileus is assuming its cap-like form, that the membrane stretching
from the stem to the edge of the young pileus is separating from the
edge of the gills, and forming a _veil_, which, in course of time,
will separate below and leave the gills exposed. When, therefore, the
mushroom has arrived almost at maturity, the pileus expands, and in
this act the vei