THALLOGENS. 255 
If we examine the soil of a truffle bed of Poitou, in the month 
of September, for instance, we find that it is traversed by great 
_ numbers of these white cylindrical threads, as fine as a sewing- 
thread, which are nevertheless composed of microscopical filaments 
some thousandth part of an inch in diameter. These threads, 
notwithstanding their minuteness, are formed of cellules, and in 
continuation with a flaky mycelium of the same nature, which sur- 
rounds the young truffles, forming round them a sort of white 
' packing, some twentieth part of an inch thick. These filaments 
connect themselves directly with the external bed of the young 
truffle. But this enveloping network is soon destroyed; at first 
slowly and ‘partially, then entirely, and the truffle appears com- 
pletely isolated in the soil. ; 
€ structure of the truffle is much more complicated than was 
formerly imagined, and we are indebted to the works of the 
Brothers Tulasne for much that we now know respecting the 
organisation of this singular vegetable. 
© young vegetables present very irregular sinuous cavities, 
partially communicating with each other, which abut, sometimes 
on aN unique opening corresponding to an exterior depression, 
Sometimes on many points of the surface. When more advanced 
mM age they are traversed by a double system of veins—the one 
white, the other coloured. The coloured veins are continued to 
the exterior tissue which composes the envelope. In their middle 
parts they are formed of a network of filaments running also in 
€ same direction, whence issue shorter filaments perpendicular 
to them, whose swelling extremities become the sporangia. The 
White veins seem to be forced by the elongation of sterile filaments 
Mtermingling with the sporangia, between which the air is found 
: oe itself. They come out on the surface in one or many 
Mts, 
The Spores, whose forms are much varied, though constant for 
the Same species, are limited in number, which rises from four 
toeight. Their external membrane is soft, downy, or reticulated. 
The Tuber brumale, milanosporum, estivum, and mesentericum, are 
‘ only Species sought for in France. 7. cebarium grows abun- 
oats mM various parts of England, where it is gathered about 
€ Size of a large walnut, having a peculiar smell, and something 
