Affinities of British Tuheraceae. 245 
mature, and, in addition, there is a distinct small opening or perforation 
in the cortex, shadowing in the structure which is characteristic of the great 
group of Ascomycetes known as Discomycetes, which originated from the 
Tuheraceae. So far as our knowledge at present goes, there is no advantage 
to subterranean Fungi in the possession of an opening in the cortex, but as 
in many other well-known instances, the presence of a structure of no 
immediate service to the members in which it originated, becomes a factor 
of primary importance to a subsequent group. Figures 16 to 19 on the 
accompanying plate illustrate the sequence of evolution from the typical 
subterranean condition of the Tuheraceae to the equally typical condition 
of the above-ground Discomycetes. In Tuber (Fig. 16), the cortex is quite 
continuous, without any opening, hence the hymenium is, as it were, hermeti- 
cally sealed until the decay of the wall of the peridium or cortex. The 
hymenium is spread over the free surfaces of sinuous plates which prac- 
tically fill the peridium. In Gene a (Fig. 17), the peridium has a small 
opening, and the hymenial plates or tramal walls do not fill the peridium to 
the same extent as in Tuber. In another species of Genea (Fig. 18), the 
opening of the peridium is still more pronounced, and the projecting tramal 
plates are almost obliterated. All the above species are truly subterranean, 
and the dispersion of their spores is effected by rodents. In Sphaerosoma 
the ascophore is only partly buried in the ground, the wall has a small 
opening, and the projecting tramal plates have disappeared, the hymenium 
lining the inside wall of the ascophore only. Sphaerosoma was until 
recently placed in the Tuheraceae, but is now considered as belonging 
to the Discomycetes. It is in reality a transitional genus, connecting the 
two families named above. Finally the genus Peziza (Fig. 19) grows 
above ground, and in the most primitive types, as the one figured, the 
ascophore is almost indistinguishable from that of Sphaerosoma, except 
in that it develops above ground, has lost the strong aroma characteristic 
of the Tuheraceae, and depends on wind for the dispersion of its spores. 
This combination of characters constitutes the group known as Disco- 
mycetes, as contrasted with those of the Tuheraceae, from which it evolved. 
The modifications necessary to enable the asci to eject their spores into the 
air, for dispersion by wind, in the Discomycetes, is contemporaneous with 
the modifications of the ascophore, already enumerated in the Tuheraceae. 
In typical members of the Tuheraceae, the asci play no part whatever in the 
distribution of the spores, hence they deliquesce and disappear at an early 
stage, liberating the spores into the cavities of the ascophore ; furthermore, 
such asci are usually globose or broadly elliptical, and contain a variable 
number of spores, and of various sizes, sometimes a single very large spore 
is present, whereas a neighbouring ascus may contain as many as six, 
or even eight spores. It is obvious that the nucleus present in such asci is 
erratic in its division. On the other hand, in those genera of the Tuberaceae 
S % 
