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288 Structural and Physiological Botany. 2 
layer; groups of gonidia becoming enclosed in peculiar 
fibrous envelopes, and, when so completely inwoven, grow- 
ing rapidly, and thus exercising a pressure on the cortex 
which ruptures it. The soredia which protrude through the 
crevices caused in this way increase in the same manner or 
eR! 
7 
develope into new individuals. In addition, Lichens are — 
also provided with spermogonia and spermatia, correspond- 
ing in all respects to those of the Ascomycetes. Finally, 
they also possess peculiar receptacles or apothecia (Fig. 409 
I1., p. 285). These are either open from the first, and then 
expand and bear the hymenial layer on their surface (Fig. 
413); or they open only at the apex by a narrow canal ; or 
Fic. 413.—Vertical section through the middle of a young apothectumn of Lecanora 
subfusca ; the club-shaped asci are developed at the apex of the ascophorous 
hyphz, and lie imbedded in the hymenium; the layers at each side contain 
spherical gonidia (x 100). 
they remain closed, and enclose a fertile nucleus. Hyme- 
nial layers of the first kind correspond to the receptacles of 
the Discomycetes, and the Lichens to which they belong . 
are called gymmnocarpous ; those of the two last kinds re- 
semble the penthecia of the Pyrenomycetes, and the 
Lichens are called azgzocarpfous. The development of the 
apothecia always begins in the interior of the thallus. 
When mature they consist of the external tissue or 
excipulum ; of a layer in which larger and stouter hyphal 
filaments are developed than those found in the remainder 
of the tissue, the ascophorous hyphe or subhymenial layer ; 
and of the true Aymenzal layer, composed of parallel hyphze — 
or paraphyses and of the ascz. These latter usually contain — 
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