34 DIVISION I.—GENERAL MORPHOLOGY. 
The medulla is surrounded at first by an inner stratum of the rind which is at 
every point firmly connected with it, and is composed of one or two layers of cells 
with contents showing no oil, and with membranes that are strongly thickened often 
more on the outside than on the inside and of a dark violet-brown colour. This inner 
stratum of the rind is,enclosed by an outer portion formed of a few or even as many 
as twenty layers of longitudinally arranged or irregular branched rows of cells; 
the cells are narrow and their membranes are of a pale violet-brown. This is the 
thin pale-violet coating, often with longitudinal stripes or interruptions, which clothes 
the surface of the fresh sclerotium and may be easily broken or rubbed off from the 
firm inner rind. 
All sclerotia, it would appear, develope as secondary formations on a primary 
sporogenous filamentous mycelium. They arise from a single branch of a mycelial 
filament which has quickly produced a tuft of many branchlets; this is the case in 
Coprinus stercorarius, Typhula variabilis, and T. gyrans. In others, as in the forms of 
Sclerotinia, several adjacent branches of the primary mycelium take part in the forma- 
tion from the first. In both cases the young sclerotium soon rises above the substratum 
as a small tuft of loosely tangled hyphal branches in all essential points similar to the 
primary. Then in Sclerotinia Sclerotiorum the filaments of the tuft grow vigorously 
and branch and coalesce repeatedly by means of H-shaped cohesions, and thus the 
tuft itself developes into a dense white ball of the size of the sclerotium ; till this size is 
reached, the structure of the hyphae remains as it was originally, the new branches 
are often slenderer than the primary hyphae and their character is uniform in all parts 
of the ball. The interstices in the tissue contain air, the surface is rendered finely 
hairy by the presence of slender spreading branchlets of the hyphae, and the whole 
body is soft and can be easily compressed into an extremely small compass. But 
from this time by new formations in its interior, and afterwards by expansion_of the 
cells already formed, the tissue constantly increases in size and firmness. Lastly the 
thickening of the membranes commences, which is characteristic of the species, and 
this is accompanied with a partial disappearance of the air-spaces and the differentia- 
tion into medullary and cortical layers. This process of development begins in the 
interior of the tissue and advances rapidly towards the circumference. The outermost 
layer of the white ball takes no part in it, but remains for a time as a white felted 
covering on the rind which is distinct from it, and ultimately shrinks to nothing and 
disappears. The ripe sclerotium becomes detached from its felted environment as a 
body of sharply defined form and outline. 
Sclerotinia Fuckeliana exhibits the same phenomena when cultivated upon a 
microscopic slide ; but, as might be expected, these are modified by the nature of its 
environment when the sclerotium is developed spontaneously inside the tissue of a 
phanerogamous plant. Peziza ciborioides also behaves in a similar manner, but shows 
some specific variations in its development. 
The tuft of hyphae which is the commencemet of a sclerotium of Typhula 
variabilis rises above the substratum in which the primary mycelium has spread its 
ramifications’. The branches of the tuft become woven together into a smooth 
white spherical body of small size, which is attached to the substratum by a short 
and slender stalk. The sphere enlarges rapidly by the formation of new cells and 

1 The substratum in the natural way of growth is formed of decaying leaves in winter and spring ; 
Brefeld employed nutrient solutions for the purpose of artificial culture. 
