204 RESEARCHES ON FUNGI 



the hymenium where spore-discharge is actively taking place as 

 the zone of spore-discharge. Such a zone may be two or more 

 centimetres long, but it is only a fraction of a millimetre wide. 

 A zone of a gill, where spore-discharge is taking place rapidly, 

 becomes entirely spore-free owing to the fact that all the basidia 

 within it discharge their spores almost simultaneously. The two 

 opposite zones of spore-discharge on a gill gradually move upwards 

 together and parallel to themselves. Thus, in the course of about 

 two days, all the spores on a gill are successively discharged from 

 below upwards. 



With the commencement of spore-discharge, or possibly just 

 previously thereto, the marginal cystidia bordering the zone of spore- 

 discharge break down, and become fluid and unrecognisable. The 

 discharge of spores leads to the production of a zone of spore-free 

 gill surface. Before this has become 0'5 mm. wide, it becomes 

 subjected to the process of autodigestion. The basidia at the gill 

 edge, which were the first to discharge their spores, together with 

 the paraphyses between them, rapidly lose their sharp contours, 

 become entirely disorganised, and turn into fluid. The subhymenial 

 cells and those of the traina break down in a similar manner. 

 Thus the gill edge, for a distance of about two centimetres, becomes 

 converted into a dark liquid film (Plate II., Fig. 8, a). We can 

 now distinguish five zones on each surface of a gill, running parallel 

 to its oblique edge (Plate II., Fig. 12). Highest of all is a zone with 

 basidia bearing ripe spores. Below this is the narrow zone of spore- 

 discharge, where the basidia are all rapidly freeing themselves of 

 their spores, by shooting them out one by one into the interlamellar 

 spaces. Further below, there is a narrow zone of spore-freed surface 

 where the basidia all have naked sterigmata. Below this again 

 is the zone of autodigestion where the basidia and paraphyses 

 are becoming disorganised and liquefied. Finally, occupying the 

 extreme gill edge, there is a dark-coloured, adhesive, liquid film. 



By watching a piece of a gill like that represented in Plate II., 

 Fig. 12, when placed in a closed compressor cell, it is easy to 

 determine that the zone of autodigestion follows hard upon the 

 zone of spore-freed surface. However, it never invades the zone 

 of spore-discharge, although it is always less than a single milli- 



