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 of a 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 labours 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 



n 2 



