CHAPTER II.—DIFFERENTIATION OF THE THALLUS.—SCLEROTIA. 31 
air-conducting passages, as in P. Fuckeliana, or with comparatively few of them. 
Its hyphae are cylindrical and septate, and interwoven with one another in every 
direction ; hence in thin sections of the sclerotia their lumina appear in all possible 
forms according as the section passes through them transversely, obliquely, or 
longitudinally (Figs. 13, 14). The cells in the moist state contain little else than 
a watery fluid; in the dry state they contain air. Towards the rind the hyphae 
are divided into short cells, and in sections therefore most of the cells have a circular 
outline. j 
The rind consists of isodiametric roundish-cornered cells which have firm dark-brown 
membranes and adhere closelyto one another. In small forms (Fig. 13) it is composed 
of one or two layers of cells, in larger (Peziza tuberosa, P. Sclerotiorum, Fig. 14) of 
three or four or more layers, and then the cells are usually arranged in irregularly 
radiating rows perpendicular to the surface. It can be easily shown in most cases 
that the elements of the rind are those segments of the medullary hyphae which lie 
nearest to the surface of the sclerotium. 
The breadth of the hyphae varies in different species and sometimes in different 
individuals. 
EN 






FIG. 13. Piece of a thin transverse section FIG. 14. Thin section through a mature sclerotium of Scterotinta Sclerotiorum, 
through asclerotium of Sclerotinia Fuckeliana ; Libert, showing the rind and adjoining medullary tissue. Magn. 375 times. 
rthe rind. Magn. 390 times. 
Many of the forms which belong to this group occur on the surface of the part of the 
plant on which they grow, others inside them in their decomposing substance. The 
former (Peziza tuberosa, and P. Sclerotiorum frequently) show the structure, which has 
been described, quite perfectly. Some of the latter, as P. Sclerotiorum, often enclose 
isolated dead cells or larger portions of the tissue of the part of the plants, which they 
inhabit, in their own substance, as Corda pointed out. The foreign bodies thus 
enclosed are irregularly and inconstantly distributed through the medulla, and 
are sometimes surrounded by a layer of dark-brown cells of the rind. 
The smaller sclerotia of this type, which are found growing on decaying leaves 
(Peziza Candolleana, Lev., P. Fuckeliana), regularly take possession of the substance 
of the leaf at the points where they are developed. They are weal-like swellings 
on the leaf, formed of the tissue-elements of the sclerotium, among which the dead 
elements of the leaf are interposed, though more or less displaced and separated 
from one another. The way in which the sclerotium takes possession of the tissue 
of the leaf is different in different species. The sclerotium of P. Fuckeliana for 
example (Fig. 19) inhabits only the parenchyma and epidermis of the leaf of the 
grape-vine, but sometimes it grows even over the hairs on the leaf and so appears 
