The Structure and Affinities of British Tuberaceae. 
BY 
GEORGE MASSEE, F.L.S. 
With Plate XVII. 
I T is a somewhat remarkable coincidence, if nothing more, that two of 
the primary divisions of the Fungi, Ascomycetes and Basidiomycetes 
respectively, should be represented by subterranean forms possessing many 
morphological and physiological features in common. Amongst such may 
be enumerated a comparative absence of differentiation, the large size and 
marked variability in the number of spores, whether produced on basidia or 
in asci, and the more or less elaborate ornamentation of the epispore. 
Hymenogastraceae, the subterranean group belonging to the Basidio- 
mycetes, is characterized by the spores being produced on basidia, whereas 
in the Tuberaceae, representing the Ascomycetes, the spores are contained 
in asci. With this marked exception the mode of development and general 
structure is the same in the two groups. 
The sporophore originates as a minute ball from a weft of mycelium, 
which is generally located some distance underground, and continues to 
increase in size for some considerable time before differentiation commences. 
During this period the sporophore consists of a solid mass of densely inter- 
woven hyphae, usually more or less globular in form, although sometimes 
lobed or irregular. At a later stage the peripheral hyphae become thick- 
walled and dark-coloured, and form the cortex, which in some species 
remains smooth and even, in others nodulose, or broken up into pyramidal 
warts. The ultimate structure of the cortex depends on the relative rate of 
growth of the peripheral and central portions of the sporophore. If the 
two portions grow at the same rate and for the same length of time, the 
cortex remains even. On the other hand, if the cortex ceases to grow and 
becomes rigid at an early stage of development, before the internal portion 
ceases to grow, the outward pressure of the latter breaks up the cortex into 
polygonal warts or pyramids, which become more or less separated from 
each other at the base, depending on the relative increase in size of the 
central mass of the sporophore. The warts and spines present on the 
[Annals of Botany, Vol. XXIII. No. XC. April, 1909.] 
S 
