302 THE MICROSCOPE. 



We cannot conclude this brief notice of the fungi with- 

 out adding a few words upon that curious group of subter- 

 ranean plants, which instead of producing their spores at 

 the summit of a basidium, or extremity of a simple filament, 

 produces them in the interior of a vesicle or pouch, called 

 a theca or ascus. Of this species the best known example 

 is the truffle (Tuber tibarium). 



It is, perhaps, not very generally known that the 

 curiously formed, irregular mass, so much esteemed for its 

 delicious taste, and sought after as a luxury, the truffle, is 

 in truth a species of mushroom ; more properly speaking, a 

 subterranean puff-ball, or fungus. Its existence, entirely 

 removed from the action of light, is an anomaly even 

 among plants of the fungus kind ; for light, although not 

 in a large degree necessary to the fungus, is almost 

 always indispensable to its full development. It would, 

 therefore, be most difficult to discover, if it were not for 

 a peculiar and penetrating odour, which dogs are taught 

 to recognise ; and by the aid of these useful animals its 

 presence is detected hidden beneath the soil. 



Tulasne and others have pointed out that these fungi 

 present two essentially different types. In the one, Hy- 

 menogastrece, the internal fleshy mass presents a number of 

 irregular cavities, lined by a membrane analogous to that 

 which clothes the gills of the Agaric, and the superficial 

 cells produce at their free extremities three or four spores, 

 or seeds, which become detached, and eventually fill up 

 the cavities. The other type, Elaphemycce, Tuberacece, 

 comprising those of the truffle kind, and as may be sur- 

 mised by the scientific name assigned to them Tuber 

 cibarium, are plants characterised from the underground 

 root presenting a fleshy mass, the outer surface of which 

 constitutes the common envelope, peridium, while the 

 numerous narrow sinuous cavities are lined and in part 

 filled up by filamentous tissue, mingled with cells of a 

 peculiar form, and terminating in spores. 



A section from, the fleshy-looking mass cut very thin 

 (Plate I. No. 2), and viewed under a power of 250 

 diameters, is found to be chiefly composed of cellular 

 substance, the interspaces of which are filled up by 

 jointed filaments, homologous to the mycelium or spawn 



