627 
Cystidia of Coprinus atramentarius. 
spores are shot forward into the interlamellar spaces for a distance of about 
01 mm., it seems clear that the cystidia are here too short to hinder the 
escape of the spores from between the gills in normally oriented fruit-bodies. 
The exact function of the cystidia of Inocybe still remains to be elucidated. 
V. Summary of the Chief Results. 
The gills of Coprinus atramentarius are of great width and of extreme 
thinness, and consequently are very flexible. Numerous long cystidia 
stretch between and connect adjacent gills, the general surfaces of which 
thus become separated by an interlamellar space about o-io mm. wide. 
The cystidia serve as props, firstly, to keep the gills from touching one 
another by their general surfaces during the development of the spores, and, 
secondly, to provide sufficient interlamellar space for the escape of the 
spores from between the gills during their discharge. 
The cystidia do not drop out of the gills when mature. Their dis¬ 
appearance is due to auto-digestion. Excluding the cystidia, the gills 
undergo auto-digestion in the manner that I have already described for 
Coprinus comatus. Each cystidium begins to undergo auto-digestion as 
soon as it comes to be situated about 0*5 mm. above the upwardly pro¬ 
gressing general zone of auto-digestion and about forty minutes or so before 
the basidia and paraphyses in its immediate vicinity. During their auto¬ 
digestion the cystidia become progressively thinner, their contents are appa¬ 
rently absorbed by neighbouring cells, and they are finally withdrawn in a 
much reduced state to the gill-sides, where their destruction is completed. 
The cystidia, owing to their early auto-digestion, never persist until the 
upwardly progressing zone of spore-discharge reaches them. Their prop- 
function, however, is retained up to the last possible moment, and they dis¬ 
appear just in time to prevent the falling spores from striking and adhering 
to them. 
In the genus Coprinus there are at least two methods of providing for 
the maintenance of interlamellar spaces: (1) the cystidia method, and 
(2) the swollen gill-margin method. The former is employed by C. atra¬ 
mentarius ,, C. narcoticus , C. stercorarius , C. fimetarius , and C. niveus , and 
the latter by C. comatus , C. sterquilinus , and C. plicatiloides. The three 
last-named species do not have cystidia on their hymenial surfaces. 
Auto-digestion of the cystidia has been observed in eight species of 
Coprinus. It seems very probable that self-destruction in connexion with 
spore-liberation is the rule for cystidia wherever they occur in the Coprini. 
Probably, throughout the Coprini, cystidia have a mechanical function 
in that they serve to prevent opposing hymenial surfaces from touching one 
another during the development of the basidia and spores, However, if so, 
this function is carried out in slightly different ways in different species. 
A certain amount of auto-digestion occurs in the small coprophilous 
