CHAPTER V. — COMPARATIVE REVIEW. — ASCOMVCETES. 223 



Pyrenula, and Polyblastia, and Krabbe's results given above make it highly probable 

 that the processes in the Lichen-fungi with which he was dealing are of a different 

 kind. 



With regard to the rest of the phenomena observed in the sporocarps of the 

 Lichens of which we are speaking, it may be remarked that apothecia as well as peri- 

 thecia are not formed on the surface as in Collema and most of Krabbe's species, but 

 inside the thallus, as in Xylaria, in the shape of coils of delicate primordial hyphae 

 which only come to the surface in the course of further development, pushing aside 

 the tissue of the thallus above them in a manner which varies with the species. In 

 species of Placodium, Lecanora, Zeora, Callopisma, Lecidea, Blastenia, Bacidia, and 

 Pannaria, which have been examined and which form apothecia, a dense tuft of slender 

 branched filaments, growing towards the outside, shoots out at an early period from 

 the whole of the upper side of the primordial coil which is turned towards the upper 

 surface of the thallus ; these filaments are the first paraphyses. An outermost layer of 

 similar filaments, open above and of varying thickness in each case, surrounds the tuft 

 of paraphyses and runs to the surface of the primordial coil; this layer is the excipulum, 

 though not exactly in the sense in which that word has been used hitherto in descriptive 

 Lichenology. The excipulum is either formed at the same time as the first paraphyses, 

 so that the outermost rows of the tuft become the hyphae of the excipulum, as in 

 Placodium, Lecanora, Lecidea, &c, or before the paraphyses as in Blastenia ferruginea, 

 Huds. according to Fiiisting. While the filaments of the primary tuft of paraphyses 

 increase in length and form new branches, which insert themselves vertically between 

 the first ones, and while the excipulum enlarges its surface in every direction by the 

 formation of new interposed hyphae and grows by the appearance of new elements at 

 its margin and of new hyphal branches continually behind the margin, which are like 

 the primary paraphyses and in contact with them on the outside, — while all these 

 processes are going on simultaneously, the young sporocarp by accession of new 

 elements increases in height and thickness. The introduction of new branches 

 continues for some time in the lower portion of the original tuft of paraphyses, and 

 in such a manner that the filaments which were at first parallel become irregularly 

 woven together, forming a tissue which cannot be distinguished from the primordial 

 coil. The formation of new elements is followed directly by increase of size through 

 expansion of the previous elements. The whole growth is first completed in the 

 middle of the sporocarp ; it continues longest, and often a long time after the 

 sporocarp has appeared on the surface of the thallus, in the upper margin of the 

 excipulum and close underneath it, where new constituents are being constantly and 

 progressively added by apposition. The ascogenous hyphae also make their appearance 

 with the first paraphyses. 



The formation of the perithecia in Lichens from the primordial coils of hyphae 

 follows in general the same course as that which has been given for Xylaria and 

 Polystigma, &c. ; but the first origin of the ascogenous hyphae is unknown. Peculiar 

 features and deviations from rule may be studied in the authors named above, 

 especially Krabbe and Fiiisting. 



Course of development of the Ascomycetes. 



Section LXV. The life-history of the Ascomycetes has been thoroughly 

 studied in the same species as the development of the sporocarps ; there are many 

 besides in which it is sufficiently known to allow of our comparing them with the 

 others and judging of them with certainty. 



The simplest case is where under normal conditions the germinating spore 

 developes directly a mycelium or thallus, which also directly produces sporocarps 

 in the modes described above, without the appearance of any other organs of 



