30 DIVISION I.—GENERAL MORPHOLOGY. 
Section VIII. The name sclerotium has been given to certain thick tuber-like 
bodies formed on the primary filamentous mycelium which proceeds from the ger- 
minating spore; these, which are storehouses of reserve-material, become detached 
from the mycelium when their development is complete, usually remain dormant 
for a considerable time, and ultimately expend their reserve-material in the production 
of shoots which develope into sporophores. 
The sclerotia are generally exposed on the surface of the substratum, or they are 
formed on the walls of broad fissures in it or sometimes even in the close tissues of 
phanerogamous plants. 
Their form and average size vary much according to the species, the latter being 
dependent also on the quantity and quality of the food supplied to them. The 
sclerotia for example of Typhula variabilis are small spheres usually of the size 
of a mustard-seed, those of Sclerotinia Sclerotiorum differ extremely in shape and 
may be smaller than a pea or as large as a hazel-nut, or form shapeless cakes some- 
times an inch in breadth; the sclerotia of species of Claviceps are horn-shaped blunt 
triangular bodies which may be more than an inch long and some millimetres in 
thickness, or scarcely 1 cm. in length and 1 mm. in breadth, according to the species 
and the nutrition. 
The structure of these bodies in their mature resting state is, in some points of 
chief importance, the same in all the species. They consist chiefly of a uniform 
compact tissue, the sedz/la, which, with a single exception noticed below in paragraph 
d, is surrounded by an outer layer of peculiar structure forming the rzzd or outer coat. 
Both parts contain comparatively little water. The medulla is a close weft of hyphae 
or a pseudo-parenchyma, the elements of which are pale-coloured or colourless and 
contain a large quantity of reserve food-material ; this in some cases takes the form of 
a great thickening along with gelatinisation of the membranes of the cells, the lumina 
of which are narrow and contain little solid matter, as in species of Sclerotinia and in 
Typhula gyrans, &c., or their cell-walls continue thin and the food-material is in the 
form of large accumulations of fatty matters, as in Claviceps, or of fine-grained proto- 
plasmic substances, as in Coprinus stercorarius and others. Exact investigation of, 
the reserve material has been made only in the case of the sclerotia of Claviceps?. 
The rind is composed of one or more layers of cells which have their membranes 
wholly or partially sclerosed and dark-coloured, and are poor in solid contents. 
Within the limits of this general structure, which is common to these bodies, 
there are special structural arrangements which vary much in the different species. 
Outward likeness is not always accompanied by agreement in their internal 
structure, which may also be like or very unlike in nearly related species, 
The following details, most of which appeared in the first edition of this work, will 
illustrate these points. 
a. The sclerotia of the Sclerotinia-Pezizeae (Peziza tuberosa, P. Sclerotiorum, 
P. Fuckeliana, P. Candolleana, P. ciborioides, P. baccarum, &c.) have a thin, black, 
smooth or rough rind, and a medulla which in the dry state is of a white or whitish 
colour. The latter is a firm gelatinous tissue of cartilaginous texture without any 

1 Flückiger, Pharmacognosie d. Pflanzenreichs ; see before on page 17. 
