884 AN INVERTKD HYMENIUM IK AGARICUS CAMPESTRIS, 



cap, however, showed it to be quite abnormal in character (PL 

 xcii., fig. 4). They showed that the "gills" had a most irregular 

 outline, that they varied much in width, and that many of them 

 were hollow. Spores in abundance were produced, both on the 

 external surface of the gills, and on the walls lining the internal 

 cavities. These spores were produced upon enlarged cells, and 

 borne upon sterigmata, as in the case of normal gills. While, 

 however, the normal number of sterigmata is four, cells bearing 

 only one, or only two sterigmata were found, as well as cells 

 bearing the normal number of four (PI. xciii., figs. 5, 6, 7). Crops 

 of mushrooms, showing the abnormal development above de- 

 scribed, are not unknown. W. A. Smith, according to Wors- 

 dell(l), found, on more than one occasion, crops of mushrooms, 

 every individual of which had an inverted cap on its surface. 

 According to Worsdell, an inverted hymenium may arise (1) 

 through the congenital formation of an inverted cap, or caps, 

 from the earliest stage onwards on the upper surface of the 

 primary cap; (2) through the formation of inverted caps by local 

 invagination of the margin of the primary one. It is held, how- 

 ever, that these two valuations really represent the same pheno- 

 menon, of which (1) represents the final and completed stage of 

 (2) arising congenitally and isolated. 



In my specimens, no trace of the formation of inverted caps 

 by local invagination could be found. Moreover careful examina- 

 tion of mushrooms in the " button "-stage showed, that these 

 irregular gill-lamellae, on the upper surface of the cap, were in 

 process of formation in the very earliest stages, and long before 

 the velum had separated from the stipe (PI. xciii., fig. 7). There 

 can, therefore, be no question of invagination of the cap in these 

 specimens. 



The question arises, what light, if any, does this inversion of 

 the hymenium throw upon the phylogeny of the Agaricacese? Is 

 it an expression of a partial reversion to an ancestial character^ 



That certain spawn has particular characters peculiar to it, is 

 the experience of professional mushroom-growers. In commer- 

 cial practice, under the influence of the atmosphere and the heat 

 of the manure-beds, the mycelium gets weaker and weaker, and 



