33^ 
THALLOPHYTES. 
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. cit). 
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 hyphag 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 
organs. 
The following account will suffice to draw attention to some of the most widely 
differing forms which are of morphological importance. 
(1) The simplest form of fructification is found in Exobasidium Vaccinii ^, the 
mycelium of which is parasitic in the leaves and stems of Vaccinium Vitts 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, Tremellineee, which grow upon dead wood or upon thö 
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 Hymenomycetes the best known and most abundant species are 
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. Usually, 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 Agaricus 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 Dcedalea 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 
^ Woronin, Bericht der naturf. Gesellsch. in Freiburg, vol. IV. 1867. 
2 See Tulasne, Ann. des Sei. Nat., 3rd series, vol. XIX. [Also, ih. ser. 5, XV, and Brefeld, 
loc. c//.] 
