CHAPTER V. COMPARATIVE REVIEW. ASCOMYCETES. XYLARIA. 217 



first bulged out a little and then gradually pierced through, so that the extremities 

 of the hyphae project above the surface (B, n). The young perithecium has 

 meanwhile become egg-shaped, its broader portion lying in the medulla being 

 the future basal part, while the narrow end which is wedged into the rind is 

 the future neck with the ostiole. The canal lined with periphyses is formed 

 at an early period in the median line of the neck in a way which has not been 

 exactly ascertained, and the elements at its circumference become thick-walled and 

 black, and hence the neck is soon surrounded by a black outer wall which is con- 

 tinuous with the cortex (q). The process of turning black progresses very slowly towards 

 the base of the perithecium and is only completed when the perithecium is ripe. After 

 the origin of the neck the basal portion of the perithecium extends itself further 

 into the medulla. Its circumference is all the time occupied by a layer of slender 

 firmly woven hyphae running parallel to its surface, and this layer is the outer 

 wall, which also becomes aftenvards thick and black. This encloses a tangled 

 mass of filaments filling the whole inner space; the component hyphae, with the 

 exception of the large cells just mentioned, remain delicate and slender and swell 

 strongly in water. The following is the result of Fisch's investigation into the further 

 development. 



The peripheral portion of the delicate hyphal weft last-named takes an active 

 part in the further growth, and developes into the thin-walled hyaline pseudo- 

 parenchymatous inner wall or subhymenial layer, which is about 6-8 layers of cells in 

 thickness. The whole of the inner surface of the wall gives rise to slender hyaline 

 large-celled paraphyses which appear at first singly but are afterwards closely crowded 

 together and converge towards the middle having walls that can swell gelatinously, 

 and also to small-celled ascogenous hyphae abundantly supplied with protoplasm, 

 which stand between the points of insertion of the paraphyses and are everywhere in 

 connection with the elements of the subhymenial layer. These hyphae do not reach their 

 full development till the inner space is quite filled with paraphyses, and they develope 

 at the cost of them. With the beginning of the formation of paraphyses, and in proportion 

 as it advances, the primordial tissue, or as much of it as has not been expended on 

 the construction of the inner wall, becomes spongy and gelatinous, and then dissolves 

 and the paraphyses take its place. The same thing happens also to the coil of large- 

 celled tissue which was merely alluded to above and must now be noticed again. In 

 its very early state, in which it was first mentioned above, it may often be easily 

 recognised as one simple row of comparatively large cylindrical cells very full of 

 protoplasm and irregularly rolled up together. In some cases it is uncertain whether 

 it is composed of one or more than one row of cells. It has an exact resemblance, 

 especially in the first case, to the ascogonium of Polystigma, but with this difference, 

 that it is always entirely inclosed in the spherical primordium, and does not send out a 

 trichogyne-process outside it. It takes no direct part in the formation of the asci 

 but, as the primordium increases in size, its coils are drawn asunder and then separated 

 into pieces by the intrusion between them of branches of the transitory primordial 

 hyphal weft. The entire coil remains inclosed in this weft and swells into a jelly and is 

 dissolved with it ; it is rare to see small portions of it taken up by the subhymenial 

 layer and withdrawn from their inevitable fate. The transverse walls in the cells of the 

 coil resist the dissolving influences longest, and even swell for a time into highly 



