CHAPTER V.—COMPARATIVE REVIEW.—ASCOMYCETES,—POLVSTIGMA. 215 
fimiseda, Peziza granulata, and P. scutellata, and by Tulasne to P. melanoloma; by 
R. Hartig to Rosellinia quercina and Nectria. 
ıo, Polystigma rubrum and P. fulvum. The thallus of these Fungi 
forms compact disk-shaped stromata in the living tissue of the leaves of species of 
Prunus. It forms spermogonia, which resemble those of Collema in structure and 
produce curved filiform spermatia. At the same time or soon after, the primordia 
of the perithecia make their appearance in its interior. These are small coils 
of closely interwoven hyphal filaments, which are perfectly similar in structure 
in their early stages and show no manner of differentiation. The individual cells 
of the coil are distinguished from those of the thallus by their small dimensions and 
especially by turning yellowish brown, not blue (see page g), with solution of iodine. 
As the growth of the coil proceeds the cells in its interior assume a more delicate 
appearance from diminution in thickness of their walls and become densely 
filled with protoplasm. A spirally coiled filament composed of broad and 
rather short cells, which comes out very beautifully when coloured with iodine, now 
becomes conspicuous among them. Its two or three turns extend through the entire 
space of the primordium, which in this stage is usually of an elongate ovoid form. 
The extremity of the filament rises above the primordium and passing through the 
cells of the mycelium penetrates to the surface of the leaf, where it finds its way 
through a stoma into the outer air, and has a perfect likeness to the apex of the 
trichogyne in the ascogonium of the Collemaceae as described by Stahl. The point _ 
is generally accompanied by more slender mycelial hyphae which grow out through 
the stoma when the trichogyne has decayed, and form a penicillate tuft of 
companion hyphae. Spermatia have been frequently seen to adhere to the summit 
of the trichogyne, but in no case has a more intimate connection, especially 
conjugation, been proved to take place. After some time the cells of the 
trichogyne-filament begin to die away from above downwards and to be no longer 
distinguishable in the tissue of the thallus, while the young perithecium enlarges at 
the same time throughout, the cells of its outer layers becoming elongated to form the 
wall, The remaining portion of the spiral filament, the ascogonium, also enlarges 
its cells considerably and now appears as a thick highly refringent strand of cells. 
In Polystigma rubrum the young perithecium remains in this state during the winter, 
but the development goes on without interruption in P. fulvum, and consists in the up- 
ward growth of the envelope in a conical form and the flattening of the basal portion 
of the young perithecium, while the inner tissue swells at the same time into a jelly. 
The ascogonium lies irregularly distorted on the base of the young perithecium. The 
hyphal weft of the base of the perithecium sends in paraphyses between the cells of 
the ascogonium in the form of thick cell-rows with walls which readily swell 
into a jelly, while the upper part of the wall of the perithecium is covered 
with periphyses. The cells also of the ascogonium, all of them apparently, 
form protuberances which elongate into slender filaments with abundance of 
protoplasm and then branch, and soon become a mass of interlacing threads 
amongst the basal tissue of the paraphyses; these are the ascogenous hyphae, 
and their last ramifications grow upwards as asci, and as they increase in 
size they displace the paraphyses, which are then dissolved. The periphyses also 
disappear, and the basal tissue of the asci and paraphyses swells up and can 
