British G astromycetes. 5 
branches of the hyphae forming the hymenium. In the 
Phalloideae and the Lycoperdeae different zones of the sub- 
vStance of the external protective layer, known as the volva in 
the former and the peridium in the latter, become remarkably 
differentiated, which results in the splitting-up of the originally 
homogeneous coat into two or more distinct layers. This may 
be due to the gelification of a middle layer, as described by De 
Bary 1 in the genus Geaster ; or to its disintegration into a 
friable powder as in Calostoma 2 . The structure of the peridium 
varies considerably in the different orders, and as would be 
expected, is least differentiated in the subterranean Hymeno- 
gastreae, where it consists of a thick comparatively homo- 
geneous, indehiscent wall, enclosing the hymenium-bearing 
portion, collectively known as the gleba. The expression sub- 
terranean, as applied to the members of the Hymenogastreae, 
means that the plants remain underground after the spores are 
mature. In the Phalloideae and some genera belonging to the 
Lycoperdeae, as Geaster , Tulostoma , Battarrea , etc., differenti- 
ation of the gleba up to the formation and ripening of the 
spores takes place while the sporophore is below the surface 
of the ground, from which it emerges for the sole purpose of 
spore dissemination, and the leading idea in the progressive 
evolution of the sporophore is that of accomplishing the above- 
mentioned function in the most effectual manner, which is at- 
tained in the Phalloideae, where the very minute spores, 
mixed with mucus resulting from the disintegration of the 
constituents of the hymenium, form a semi-liquid, strong- 
smelling mass, greedily sought after and devoured by flies, by 
whose agency the spores are dispersed. The genera Sclero- 
derma and P olysaccum form a transition from the subterranean 
forms to those that emerge above ground when mature, and in 
these genera the peridium is structurally but little in advance 
of that of the Hymenogastreae. 
There is much less variety in the arrangement of the 
1 1. c. p. 316. 
2 G. Massee, A Monograph of the genus Calostoma, Desv. ( Mitremyces , Nees) ; 
Ann. Bot.. vol. ii. pp. 25 -45, PI. III. 
