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. 



The rind consists of isodiametric roundish-cornered cells which have firm dark-brown 

 membranes and adhere closely to 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. 



FIG. 13. Piece of a thin transverse section 

 through a sclerotium of Sclcrotinia Fvckcliana \ 

 r the rind. Magn. 390 times. 



FIG. 14. Thin section through a mature sclerotium of Sclcrotinia Scltrotiont'fi 

 Libert, showing the rind and adjoining medullary tissue. Majjn. 375 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 



