Cystidia of Copr inns atramentarius . 623 
out touching one another, and (2) sufficient room for the violent discharge 
of the spores in the region of spore-discharge. As I have pointed out 
elsewhere, the spores of all Hymenomycetes, when moist, are very adhesive 
and, when brought into contact with one another, stick together. If the 
spores on basidia of opposing gills were to touch one another during 
development, it is probable that during the subsequent expansion of the 
pileus they would pull one another off the sterigmata, with the result that 
later on they would not be properly liberated. However, whilst the spores 
are ripening, opposing hymenial surfaces are entirely prevented from coming 
into contact with one another owing to the fact that they are propped apart 
by the numerous cystidia. 
The interlamellar spaces seem to be somewhat too wide, if we are to 
suppose that their one function is to provide space for the free development 
of the basidia and spores (cf. PI. LI, Fig. 19). However, from my studies 
of the mode of spore-discharge in the Coprini and in the Hymenomycetes 
generally, it has become clear that the interlamellar spaces require to be 
sufficiently broad to permit of the spores being violently discharged into 
them without any risk of their striking and adhering to the opposing gills 
towards which they are propelled. The spores of Coprinus atramentarius 
are shot forward from the basidia for an average distance of the order of 
0-05 mm. before they begin to fall vertically downwards. Each interlamellar 
space, in order to permit of successful spore-discharge, must therefore have 
a minimum width just exceeding 005 mm. The actual width of the spaces 
just exceeds o-io mm. It appears probable, therefore, that with the 
allowance of a slight margin of safety, the width of the interlamellar spaces 
is reduced to a minimum with due regard to the liberation of the spores. 
Since the width of the spaces is determined by the length of the cystidia, we 
may conclude that the length of the cystidia is correlated with the width of 
the space between the gills required for the violent discharge of the spores 
in the region of spore-discharge. 
From the facts which I have now recorded it seems clear that the 
cystidia of Coprinus atramentaruis are fitted for their prop function by 
their structure, size, position, number, and early development, whilst the 
time, order, and mode of their destruction are arrangements which prevent 
their becoming obstacles to the escape of the spores from the fruit-body. 
Even if we were to search throughout the whole range of the vegetable 
kingdom, it would be difficult to find any more beautiful and perfect 
example of cellular specialization and adaptation of structure to function 
than is here afforded us. 
III. General Remarks on Coprinus Fruit-bodies. 
It was pointed out in the introductory remarks that whereas Coprinus 
atramentarius is provided with numerous cystidia on its general gill- 
