274 RESEARCHES ON FUNGI 



element seen from above is or is not an exhausted basidium. A 

 basidium which has shed its spores on the first day of spore-discharge 

 is perfectly recognisable as an exhausted basidium on the last day 

 of spore -discharge, i.e. after an interval varying from about a week 

 to eleven days ; for, even then, it still retains its concave end in 

 which may be seen more or less distinctly the four sterigmatic 

 stumps. We are thus provided with a clue which enables us to 

 distinguish past-generation basidia from present-generation basidia 

 which are bearing spores, and from future-generation basidia which 

 are as yet spore-less. 



In studying the arrangement of the hymenial elements, it is best 

 to begin with a surface view and to use only living material. Fixing, 

 staining, and sectioning with the microtome, the method which has 

 proved so valuable for research in plant histology generally, is here 

 of little or no use owing to the fact that, when a hymenium has been 

 killed, the basidia and paraphyses lose their turgidity and, therefore, 

 do not stand out so sharply as when they are living. Moreover, 

 in a microtome section, one finds that most, if not all, of the older 

 spores, i.e. those which are in a state of development a little prior 

 to their discharge, have been separated from their sterigmata. In 

 making a preparation, it is best to take a gill straight from a fruit- 

 body growing under as natural conditions as possible. For my 

 investigations, gills were removed, as required, from fruit-bodies of 

 Panaeolus campanulatus growing on horse dung in the laboratory. 

 When a gill had been procured, it was placed flat on a glass slide 

 and covered with a cover-glass. A drop of water was then placed 

 at the edge of the cover-glass, under which it was sucked by capillary 

 attraction. As it passed slowly over the upper hymenial layer, in 

 several places it left the spores standing undisturbed on their sterig- 

 mata and did not drag them all off as it usually does under similar 

 circumstances in Coprini and some other Agaricineae. By mount- 

 ing a living gill in the manner just described, it became possible for 

 me to observe all the basidial elements as they are in nature. It 

 was sought not merely to get a general impression of the arrange- 

 ment of the elements on different areas of the hymenium but, more 

 especially, to find the exact arrangement of the elements on one 

 particular area. Therefore my attention became concentrated on 



