CHAPTER V.—COMPARATIVE REVIEW.—ASCOMYCETES. 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 tothe 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 Füisting. 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 
