PSALLIOTA CAMPESTRIS 361 



of the Mushroom as possible, always bearing in mind that the one 

 dominant function of the fruit-body is the production and liberation 

 of spores. This account will necessarily involve a repetition of a 

 number of statements which have been made in connection with other 

 representatives of the Panaeolus Sub-type, as well as of observations 

 scattered through the pages of Volume I. The reader who is chiefly 

 interested in the systematic description of the Aequi-hymeniiferous 

 and Inaequi-hymeniiferous Types and of their Sub-types is there- 

 fore advised to pass over this Chapter and leave it to those who 

 wish to increase their knowledge of a particular species. Among 

 the new details of hymenial organisation which will be dealt 

 with in the following pages may be mentioned : (1) the relation 

 between the hymenium and the subhymenium, (2) the structure 

 of monosporous and of bisporous basidia, (3) the arrangement 

 of the spores on two adjacent bisporous basidia, and (4) the 

 disappearance of exhausted basidia in late stages of hymenial 

 activity. Also included in this Chapter will be found a new dis- 

 cussion of the form of the pileus, the stipe, and the gill-system, 

 which is of general application to the Agaricineae. 



In endeavouring to elucidate the organisation of the Aequi- 

 hymeniiferous Type, my first attempts, made in 1911, were directed 

 to the cultivated Mushroom. These partially failed owing to 

 difficulties connected with the small size of the hymenial elements. 

 I therefore turned my attention to Panaeolus campanulatus and 

 Stropharia semiglobata, in which the basidia and paraphyses are 

 relatively large ; and with these species my efforts, as we have seen 

 in Chapters X and XI, were rewarded with a full measure of success. 

 In 1916, I renewed my studies of the Mushroom ; and, in the light 

 of a wide experience of hymenial organisation gained in the pre- 

 vious five years, I at once perceived that the fruit-bodies of this 

 fungus have an organisation similar to that of the Panaeolus Sub- 

 type. The magnification of the microscope used in working out 

 the finer details of structure in the gills of Panaeolus campanulatus 

 and Stropharia semiglobata had been 440. Now the diameter of 

 the basidia of Psalliota campestris is only about one-half that of 

 the basidia of those two species. In investigating the hymenium 

 of the Mushroom, therefore, it became necessary at least to double 



