PSALLIOTA CAMPESTRIS 417 



minutes it collapses, its end becomes concave, and it is drawn down 

 to the general level of the hymenium. A past-generation basidium 

 \vli ich has two sterigmatic stumps in its concave end has been 

 derived from a basidium that was bisporous ; but one which has 

 only one such stump, as shown at cm, has been derived from a 

 monosporous basidium, such as in m. The basidium-body of each 

 present-generation basidium is shaped more or less like a club 

 with the swollen end directed outwards. This swollen end pro- 

 trudes slightly above the general level of the hymenium and there- 

 fore hides to a greater or less extent the immediately adjacent 

 past-generations basidia, future-generations basidia, and para- 

 physes. Owing to this fact, the optical difficulties in making out 

 the structure of the hymenium in surface view are considerably 

 increased. The amount of massive protoplasm inside the body 

 of a present-generation basidium, i.e. all the protoplasm except 

 a very thin layer lining the walls which probably remains until 

 the basidium collapses and dies, varies greatly in correspondence 

 with the age of the spores. When the spores are just beginning 

 their development on the ends of the sterigmata and are the merest 

 rudiments, the basidium-body and sterigmata are filled or almost 

 completely filled with protoplasm ; but, as the spores grow in size 

 and for several hours after they have attained their full size, and 

 even whilst they are undergoing pigmentation, the protoplasm flows 

 through the sterigmata sporewards. This progressive evacuation of 

 the basidium-body continues until the spores are ripe and ready to be 

 discharged, and it is only then that the basidium-body and sterig- 

 mata appear transparent and empty of solid contents. As the massive 

 protoplasm moves out of the basidium, its place is taken by cell-sap. 

 The coming-generation basidia, c c, are the basidia which are 

 destined to produce a new crop of spores as soon as the crop 

 upon the present-generation basidia has been discharged and the 

 basidium-bodies of these elements have collapsed and sunk down 

 to the general level of the hymenium. As soon as the present- 

 generation basidia begin to develop spores, certain other basidia 

 in their immediate vicinity become clearly marked out as their 

 successors, i.e. as the coming-generation basidia, by their rapidly 

 increasing size and prominence, and by the fact that they are 



VOL. II. 2 E 



