304 THE ESSEX NATURALIST
truffles belonging to the large genus Tuber, for example,
the apothecial structure of the fruit-body is not at all obvious
and the asci are not cylindrical. Tuber aestivum is a striking
example. This is the biggest of the British truffles. A large
specimen may weigh six or seven ounces. When immature,
this and other truffles have little smell, but when mature the
odour is strong and unpleasant. A large ripe truffle brought
into the house soon can be smelt in every room. The
mycologist bringing one into the home is soon forced to
remove it by an infuriated wife. I used to have considerable
respect for dogs and pigs that had been trained to locate
truffles. Now, after my own experience of ripe truffles, my
respect has gone—I am sure I could locate a ripe truffle by
scent alone as well as any dog or pig. Obviously, it is of
considerable biological importance that the odour develops
only when the fruit-body is ripe. Otherwise, unripe speci-
mens would be grubbed up and devoured by rodents before
their time. Presumably, the spores of truffles pass uninjured
through the animal, and in this connexion the thick spore-
walls are probably significant, but we really know next to
nothing about the dispersal of truffle spores or of their ger-
mination. Indeed, in most species the spores have never
been germinated.
There are many hypogeal fungi classified in Tuberales
which is considered to be an order of the Discomycetes, but
students of the order consider that the development of the
underground habit has not been along a single line of evolu-
tion from epigeal types. Continental mycologists recognise
at least three lines. It seems quite clear that both in
Ascomycetes and in Basidiomycetes the hypogeal habit has
been developed over and over again.
Going to earth means much greater modification than does
descending into water. No longer can violent discharge of
spores occur and no longer is there a surrounding fluid
through which liberated spores can be dispersed. Rodents
have to be called in to do the job.
One final point I must make. One would have thought
that a Cup Fungus was an excellent and adequate
mechanism for the production and dispersal of spores. But
quite a number of Discomycetes have gone to the trouble