264 RESEARCHES ON FUNGI 



One practical difficulty in observing the hymenium, and the 

 manner in which it was overcome, may here be mentioned. At 

 first, when the gill surface was focussed, the basidia and their 

 spores could be clearly seen : their definition was sharp. However, 

 it was soon found that the cover-glass (Fig. 91, Cg) often became 

 fogged owing to the condensation upon it of water-vapour trans- 

 pired from the pileus. When this fogging occurred, the hymenium 

 seen through the microscope presented nothing but a blurred 

 appearance. The removal of the water drops was readily effected 

 with the aid of a darning needle. This was taken in a pair of 

 forceps, heated for a short time in the flame of a spirit lamp, and 

 then rubbed two or three times over the outer surface of the cover- 

 glass. In a few seconds the film of moisture evaporated, and then 

 the hymenium could be seen clearly again. As this clearing 

 operation was always performed with care, the gill (the surface 

 of which was about 2 mm. distant from the cover-glass) was never 

 injured or its continuous development disturbed. 



Observations on the Developing Hymenium. The horizontal 

 microscope was at first moved about in front of the gills to be 

 observed until the middle of its field came to include what might 

 be termed a black island, i.e. a black area of the hymenium very 

 much resembling that in the centre of Fig. 89 (p. 257) but 

 practically surrounded by a white area. This black area, upon 

 which my attention became concentrated, was about 1 mm. wide, 

 and had a peculiar outline by which it could be recognised again 

 after any break in observation. Its sole spore-bearing elements 

 consisted of about 150 mature basidia, each bearing four black 

 spores. These basidia, collectively, therefore appeared to make 

 up a single generation of approximately equal-aged members. 



A few minutes after the black area just described had been 

 focussed, it was noticed that at the periphery of the area some 

 of the basidia were discharging their spores. Each basidium shot 

 off its four spores in succession. Sometimes this process took less 

 than five minutes, but sometimes longer. Since the gill had its 

 natural orientation, the spores, on being discharged into the air, 

 did not fall on to the hymenium again, but settled at the bottom 

 of the dish. After a little while, spore-discharge became general 



