be seen in the
stellate form of the conidia of _Nyctalis_.

It is almost always the external membrane that is coloured, which is
subject to as much variation as the form. The more fine and more delicate
shades are of rose, yellow-dun or yellow, violet, ashy-grey, clear
fawn colour, yellow-orange, olive-green, brick-red, cinnamon-brown,
reddish-brown, up to sepia-black and other combinations. It is only by
the microscope and transparency that one can make sure of these tints;
upon a sufficient quantity of agglomerated spores the colour may be
distinguished by the naked eye. Colour, which has only a slight
importance when considered in connection with other organs, acquires
much in the spores, as a basis of classification.

With the growth of Agarics from the mycelium, or spawn, we are not
deficient in information, but what are the conditions necessary to
cause the spores themselves to germinate before our eyes and produce
this mycelium is but too obscure. In the cultivated species we proceed
on the assumption that the spores have passed a period of probation in
the intestines of the horse, and by this process have acquired a
germinating power, so that when expelled we have only to collect them,
and the excrement in which they are concealed, and we shall secure a
crop.[C] As to other species, we know that hitherto all attempts to
solve the mystery of germination and cultivation has failed. There are
several species which it would be most desirable to cultivate if the
conditions could be discovered which are essential to germination.[D]
In the same manner the _Boleti_ and _Hydnei_--in fact, all other
hymenomycetal fungi, with the exception of the _Tremellini_--still
require to be interrogated by persevering experiment and close inquiry
as to their mode of germination, but more especially as to the
essential conditions under which alone a fruitful mycelium is
produced.

[Illustration: FIG. 79.--(_a_) Basidia and spores of _Exidia spiculosa_;
(_b_) Germinating spore.]

The germination of the spore has been observed in some of the
_Tremellini_. Tulasne described it in _Tremella violacea_.[E] These
spores are white, unilocular, and filled with a plastic matter of
homogeneous appearance. From some portion of their surface an
elongated germ filament is produced, into which the contents of the
reproductive cell pass until quite exhausted. Other spores, perhaps
more abundant, have a very different kind of vegetation. From the