EXPLANATION OF THE DRAWINGS

Enlargement = 1100

FiG. 1. — The ascospore of Iho truftle at the beginning of the germination; tlie external cellular membrane wliich is brown and covered over with prickles, is reabsorbed on the side of the spore, at an equal distance from the two pôles. The way in which this envelope is destroyed allows of its structure being distinguished : it is formed of a layer of polyhedric cells, the prickles which covered over the spore rise to the points of intersection of the cells; the external surface of thèse cells is covered over, as well as the prickles, by a tliick ))ri)vvn layer.

When the membrane is being reabsorbed, the prickles at first become dull, and blunt, in such a way as to form small rounded nipples then, according as the brown layer is dissolved, there may clearly be seen the cellulai' constitution of the membrane, which is light yellow, such being the colour of the cells.

FiG. 2-3. — The external membrane is completely reabsorbed over a certain surface and its cellular tissue destroyed. The germinal ampulla which was inside the ascospore, and which is limited by a colourless membrane projects outside the rigid brown envelope surrounding it : in its growth it tends to become spherical in form.

FiG. 4-5. — Section view of the ascospore at the moment of the extension of the internai gei'niinal ampulla, the external membrane is thicker in the vicinity of the pôles of the spore than on the rest of the circumference : the cellular structure may easily be distinguished.

FiG. 6. — A germinal ampulla which bas dilated and still bears on its surface a few un-reabsorbed nipples, coming from the extenial brown envelope of the spore.

FiG. 7. — During the growth of the germinal ampulla, the external envelope which lias not been reabsorbed, bas remained applied on the membrane of the ampulla : it is thus rejected to the back of the sphère formed by the extension in one direction of the ampulla. The reabsorption of the brown envelope continuing, there soon remains nothing of the latter except two hemispherical calottes, separated from one another and

joined to the sphère; they spring from tlie parts of the external membrane which were at the pôles of the ascospore.

FiG. 8-9. — View of the sphère produced by the growth of the germinal ampulla (this is the oogone) and of the hemispherical calottes (antheridies) which come from one part of the external membrane of the ascospore. The oogone is coloured light yellow, ils membrane présents, on the cxterior, a very finely shagreened aspect. The antheridies are completely freed of the brown matter and of the prickles which covered over the cellular layer of the external envelope of the spore. The colour of the antheridies is light yellow after the colour of the cells which compose their coating.

FiG. 10. — The oogone and the antheridies seen in section : one can distinguish the openings which hâve been made in the membrane of the oogone and which allow of communication between the latter and the antheridies. The antheridies circumscribe a cavity between their coating and the membrane of the oogone.

FiG. 11-12. — Development of the egg in the oogone.

FiG. 13. — The oogone containing an egg; in Ihe centre of the egg is found a cavity indicating that the egg has been developed by the growth of a filament, which has increased in every direction, by bending over. The antheridies hâve become detached; on the circumference of the membrane of the oogone may be distinguished three openings whence will issue the germinal filaments sent out by the egg : two of thèse openings communicated with the antheridies.

FiG. 14. — A free oogone before the formation of the egg.

FiG. 15. — The oogone and the antheridies seen transparently; in the interior, a fullydeveloped egg. The cells of the egg, regular and oval-shaped, appear as spores ; this aspect is caused by an optical illusion, for the filaments are seen in diameter; it is, indeed, possible to see certain filaments longitudinally, by causing the point to vary.

There may be seen, transparently, under the membrane of the antheridies, the two openings of the oogone opposite to tlie antheridies : a central opening is also formed at the exterior of the oogone.

The egg is brought together again at the centre of the oogone and leaves ail around an empty space in the oogone.

FiG. 16. — An egg in which may be seen the terminal filaments, ail mixed up (germinal filaments).

FiG. 17. — The central opening of the oogone; there may be several of thèse, without counting those of the antheridies.

FiG. 18. — \n oogone of very small dimensions, from which issue the germinal filaments which are the terminal ramifications of the egg.

FiG. 18' and 18'. — The same oogone seen transparently, at différent planes, so as to allow of one's observing the constitution of the egg which is very simple.

FiG. 19. — Small spherical bodies, regular and yellow, coming from the crushed oogone : they seen to be oosphères. They are bound together by a délicate and extremely thin ligament.

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