^^6 THA LL OPHVTES. 



this case also into two principal stages, the first being that of a filamentous mycelium 

 derived from the spores, the second, that of a fructification of solid tissue pro- 

 ducing numerous spores. No other organs of reproduction are known to recur with 

 certainty in the Basidiomycetes (see De Bary, loc. ciL). 



The external form and the internal structure of these fructifications vary to 

 a very great extent, but the formation of the spores takes place upon one common 

 plan. Certain branches of the fertile hyphae become swollen so as to be club- 

 shaped, and constitute the cells which bear the spores, the Basidia. Each basidium 

 produces simultaneously two or more, usually four, basidiospores (or even eight). 

 They are formed by the outgrowth of the wall of the basidium into delicate papillae 

 which become spherically or ovally dilated at their free ends : each of these dilata- 

 tions becomes invested by a firm membrane, and is a spore which remains for a time 

 upon the pedicle but at length falls off. 



The basidia are developed simultaneously in large numbers and are usually 

 closely arranged parallel to each other ; in this way the hymenia are formed, which, 

 among the Hymenomycetes, contain, as in the Discomycetes, sterile cells (para- 

 physes) among the fertile ones (basidia). If the hymenial layer clothes its free 

 external surface, the fructification is said to be gymnocarpous ; if, however, it lines 

 cavities within its tissue, the fructification is said to be angiocarpous. 



The majority of Basidiomycetes grow upon humus, or soil containing decaying 

 vegetable matter; some develope their mycelium in old wood, as in the cortex 

 of living tree-trunks ; the smaller forms use fallen leaves and decaying branches as 

 their substrata. More rarely they occur as true parasites upon living vegetable 



The following account will suffice to draw attention to some of the most widely 

 differing forms which are of morphological importance. 



(i) The simplest form of fructification is found in Exobasidium Vaecinii^, the 

 mycelium of which is parasitic in the leaves and stems of Vaccinium Vttis idcea. On 

 the surface of the organs which it has attacked, the mycelium directly bears a hyme- 

 nium consisting of closely-packed basidia, each bearing four spores. 



(2) The gelatinous Fungi, TremellineaB, which grow upon dead wood or upon the 

 trunks of old living trees, produce fructifications of a gelatinous consistency and of 

 irregular form, usually occurring as thick rugose incrustations. The delicate hyphae 

 run in the gelatinous mass and form the hymenia at the surface. The formation of the' 

 spores takes place in a more complicated manner than in the other Basidiomycetes ^. 



(3) Among the Hym.eiiom.ycetes the best known and most abundant species ar^ 

 those commonly known as Mushrooms. The structure which is usually called the Fungus 

 is the fructification which springs from a mycelium vegetating in the ground, or on wood 

 or some other substance. Usualhy, but not always, the cap [pileus) is stalked ; on its under-- 

 surface the hymenial layer lies upon projections of the substance of the pileus of various^ 

 forms. In the genus Agarlcus these projections consist of numerous lamellae attached 

 vertically and running radially from the summit of the stalk to the margin of the pileus ; 

 in Cyclomyces the lamellae form concentric circles ; in Polyporus and Doedaka they ana- 

 stomose in a reticulate manner ; in Boletus they form closely crowded vertical tubes ; in 

 Fistulina the tubes stand alone; in Uydnum the lower side of the pileus is covered with soft 



* Woroniii, Bericht der naturf. Gesellsch. in Freiburg, vol. IV. 1867. 



^ See Tulasne, Ann. des Sci. Nat., 3rd series, vol. XIX. [Also, ih. ser. 5, XV, and Brefeld, 

 loc. c//.] 



