r suggests that they may be
excitatory organs for the dehiscence of the asci. However this may be,
some mycologists are of opinion that, at least in some of the
Ascomycetes, the paraphyses are abortive asci, or, at any rate, that
abortive asci mixed with the paraphyses cannot be distinguished from
them.

The mucilage forms itself almost at the same time as the paraphyses,
and previous to the formation of the asci. This substance appears as a
colourless or yellowish mucilage, which envelopes the paraphyses and
asci, and so covers the hymenium with a shining coat.

The asci appear first at the base of the paraphyses, under the form of
oblong cells, filled with colourless protoplasm. By rapid growth, they
soon attain a considerable size and fulness, the protoplasm being
gradually absorbed by the sporidia, the first indication of which is
always the central nucleus. The mucilage also partly disappears, and
the asci, attaining their maturity, become quite distinct, each
enclosing its sporidia. But before they take their complete growth
they detach themselves from the subhymenial tissue, and being
attenuated towards their base, are forced upwards by pressure of the
younger asci, to, and in some instances beyond, the upper surface of
the disc. This phenomenon commences during the night, and continues
during the night and all the morning. It attains its height at
mid-day, and it is then that the slightest breath of air, the
slightest movement, suffices to cause dehiscence, which is generally
followed by a scarcely perceptible contractile motion of the
receptacle.

[Illustration: FIG. 34.--Asci, sporidia, and paraphyses of _Ascobolus_
(Boudier).]

There is manifestly a succession in formation and maturity of the asci
in a receptacle. In the true _Ascobolei_, in which the sporidia are
coloured, this may be more distinctly seen. At first some thin
projecting points appear upon the disc, the next day they are more
numerous, and become more and more so on following days, so as to
render the disc almost covered with raised black or crystalline
points;[z] these afterwards diminish day by day, until they ultimately
cease. The asci, after separation from the subhymenial tissue,
continue to lengthen, or it may be that their elasticity permits of
extension, during expulsion. Boudier considers that an amount of
elasticity is certain, because he has seen an ascus arrive at
maturity, eject its spores, and then make a sharp and consider