622 
Bulky .— The Function and Fate of the 
only to see the cystidia stretching across the interlamellar spaces but also 
to observe their disappearance. 
About o*5 mm. above the extreme edge of each gill where the liquid 
products of auto-digestion are adhering, the cystidia can be seen in the first 
stages of their disappearance. This is indicated by a slight diminution in 
their diameters. Nearer to the auto-digesting gill-edge the cystidia are 
seen to have become very much reduced in diameter (PI. LI, Fig. 19, zone b). 
Still nearer to the gill-edge they are seen to have become detached from 
one gill and to have become partly withdrawn to the other gill, usually to 
the one from which they originated. Sometimes, however, they can be 
seen to be broken in two either in the middle or at one end. The cystidia 
which are just above the zone of spore-discharge are reduced to practically 
nothing, so that it is difficult or impossible to detect any trace of them. 
The disappearance of individual cystidia was observed in a considerable 
number of instances. Stages in the auto-digestion of six cystidia are shown 
in PI. LI, Figs. T3 to 18. The time which elapsed between the initial 
shrinking of a cystidium and its total disappearance was found to be less 
than half an hour. It took ten minutes for the cystidium represented in 
Fig. 15 to pass from the fully turgid condition to the final stage shown, and 
the break in the cystidium represented in Fig. 16 occurred fourteen minutes 
after the initial thinning was detected. 
One may ask: what becomes of the fluid which is liberated from 
a cystidium during its auto-digestion ? It is possible that part of it simply 
evaporates, but I think it very probable that much of it is absorbed by the 
subhymenial cell with which the cystidium is connected and by other cells 
in its immediate vicinity. At first the cystidium only becomes thinner but 
retains its form. Probably at first, therefore, the cystidium cell-sap is merely 
transferred to other cells and the cystidium wall settles down over its 
diminishing fluid contents. If there were no absorption of the kind I have 
just suggested, whenever, owing to saturation of the air with water vapour, 
evaporation was brought to a standstill, the cystidium on its dissolution 
would form a large drop on the hymenial surface which would surely spread 
over some of the neighbouring basidia and prevent the liberation of their 
spores. However, in order to decide quite definitely what becomes of the 
cystidium products, some further investigations will need to be undertaken. 
The disappearance of the cystidia from the gills is so well timed that 
it seems certain that it is a regulated process. Where the stimulus comes 
from which acts upon the protoplasm of a cystidium and thus indirectly 
initiates its auto-digestion, is at present uncertain. Possibly, when a basidium 
is discharging its spores, it sends out messages to all the cystidia within 
a certain radius commanding their self-destruction. 
The existence of the interlamellar spaces between the gills provides 
(1) a space in which the basidia of opposing gill-surfaces can develop with- 
