CHAPTER II.—-DIFFERENTIATION OF THE THALLUS,—SCLEROTIA, 35 
branches in all its parts. It is entirely formed at first of uniform thin-walled much 
branched hyphae, which are rich in protoplasm and closely woven together, but not 
without air-spaces. Those parts only of the hyphae which form the outer moist surface 
of the sphere have no interstices between them ; if we examine a sclerotium in a very 
early stage of its development we see that the surface is formed ofa layer of short cells of 
uniform height, which are segments of hyphal branches running in numbers through 
the periphery. These cells are at first thin-walled and filled with protoplasm, like 
the other portions of the hyphae, and their walls are colourless. Growth by 
formation of new hyphal branches continues for some time longer in the centre of 
the sphere, and thus the medulla enlarges its circumference considerably, while its 
hyphae grow to twice their original size ; but the intertwining of the hyphae remains as 
it was before. From an early stage in the development no new cells are introduced 
between the previously existing cells of the superficial layer ; but these cells stretch in 
every direction, and sufficiently strongly in that of the surface of the sphere to remain 
united together into a layer without interstices. Their radial or lateral walls assume 
in this way the undulated inflated outline mentioned above in paragraph /, while their 
outer membrane becomes thickened to form the covering described in the same place, 
and takes the permanent yellow colour or passes through yellow and brownish yellow 
to a dark brown; the protoplasm disappears. This formation of rind is continued 
also at the point of insertion of the stalk over a layer of cells which lies in the 
direction of the surface of the sphere, and the sphere is thus divided off from the stalk 
and is ultimately detached from it, while the stalk dries up. The development of 
Typhula gyrans follows a similar course. All that is known of the development of 
other sclerotia, excepting that of Claviceps, agrees with the processes above described, 
-though the final differentiation is accompanied by certain variations in detail, as will be 
inferred from the statements in paragraphs a to g; in this matter Brefeld’s careful 
description of Coprinus stercorarius should be consulted. 
The sclerotia, of the development of which we have been speaking, are not all 
formed on morphologically definite spots of the primary mycelium, and their number 
varies according to the state of its nutrition. When several begin to be formed 
near each other, they may unite as they grow into one body; this leads to 
the formation of the irregular cakes and crusts mentioned above, especially in 
Peziza Sclerotiorum, though it is observed in other species also, as in Coprinus 
stercorarius, and in a less degree in Typhula gyrans. Much water is expelled from 
all the above sclerotia when the differentiation and final development commence in 
them, and appears on their surface in large clear drops. The whole process of 
development may under favourable conditions be accomplished from beginning to 
end in a few days. 
The sclerotia of Claviceps (ergot), concerning which Tulasne’s !zbours have given 
us more exact information, show several variations of detail in their development arising 
from the peculiar parasitism of the Fungus (Figs. 16,17). The primary mycelium 
occupies at first the base of the young ovary in the flower of the Gramineae and 
Cyperaceae. In ordinary cases, to which we will at present confine our attention, it 
spreads rapidly through the entire ovary, with the exception of its apex and some- 
times also of the inner layers of its wall; the ovary is thus changed into a white 
Fungus-body of nearly its own shape, with a surface marked with deep narrow 
D2 
