196 



DIVISION II. COURSE OF DEVELOPMENT OF FUNGI. 



With respect to the more minute anatomical structure of the Tuberaceae, it may be 

 further added, that the peripheral layer, known as the peridium, is usually a stout, 

 thick mass of pseudo-parenchymatous tissue. The outer cell-layers are in most cases 

 furnished with thickened walls corresponding in colour to the surface, which varies in 

 shade from brown to black ; in a few cases they are thin-walled and have their surface 

 covered with spreading hairs, as in Tuber" rapaeodorum, &c. Except in Stephensia, 

 in which the layers of the peridium are distinctly separated from each other, the outer 

 cell-layers pass gradually into the inner and these in like manner into the sterile veins 

 and bands which spread between the fertile tissue, and which either show the same 

 pseudo-parenchymatous structure as the peridium (Genabea) or, as in most cases, have 

 their hyphae disposed in a course which follows that of the veins. Here too ascogenous 

 hyphae appear in the tissue known as the fertile tissue interwoven with but strictly 

 distinct from other hyphae which may.be termed paraphyses. Moreover it often occurs, 

 both in Tuber and Elaphomyces, that a young ascus is placed on a knee of the hypha 

 which bears it in such a manner that it seems to be borne on two small stalks, some- 

 what as in Eremascus which will be described below. Tulasne has given representations 

 of this phenomenon, and Dr. Errera has recently called my attention to it. It may at 



FIG. 91. Tuber rufum. a small specimen divided in half in reflected light : the white veins / contain air, the dark ones v 

 fluid, A the hymenial tissue. * a thinner section through a young specimen in transmitted light ; lettering as in a, light and dark 

 appearance of the veins reversed, a magn. 5 times, b 15 times. 



least be a question whether the development of the ascus in these cases is the same or 

 similar to that of the ascus in Eremascus ; the whole subject requires investigation. 



The genera Hydnocystis, Hydnotria, and Genea are not noticed here because a 

 full consideration of them would lead us too far into descriptive details, and we must 

 be satisfied with remarking that they are intermediate in their whole structure between 

 Tuberaceae and typical Discomycetes, especially the Pezizae ; they are evidently 

 closely related to both groups. 



We are indebted to Tulasne for the little that we know of the origin of the sporo- 

 carps in Tuber, and from this they would appear, as has been already stated, to be 

 formed inside a mycelial weft. The different regions and tissues are differentiated in 

 them while they are still quite young ; the surface of specimens of Tuber mesentericum 

 of the size of hemp-seed has the same structure and the same black colour as in those 

 which are fully grown. Very little more is known than this. We shall have to wait for a 

 complete knowledge of the history of development in these subterranean plants till we 

 have succeeded in cultivating them. 



3. Onygena corvina, A. S. grows on the feathers of birds of prey and the 

 mycelium which spreads in them produces stalked spherical sporocarps. The stalk is 

 7-10 mm. in length and about I mm. in thickness, and consists of longitudinally parallel 



