The Origin and Development of the Apothecium etc. 
413 
subterminal cell is binucleate, and it is from this cell that an ascus 
develops. 
For a large number of aseomycetes it bas been ghown that the origin 
of the ascogenous hyphae is different from that of the enveloping sheath 
of vegetative hyphae. Schwendener (73 a) in 1864 was the first to 
suggest this separate origin of asci and paraphyses. In Collema micro- 
phyllum, Stahl was able to make certain that the hyphae which sheath 
the ascogone do not arise from it, but was uncertain whether they arise 
from the hyphae bearing the ascogone or from neighboring hyphae. In 
the heteromeric lichens which he studied, as well as in Pannaria , Ileppia, 
and Hydrothyria, Sturgis (76) found no differentiation of the hyphae 
into an ascogenous and an enveloping System; asci and paraphyses have 
the same origin. In the Collemaceae, Sturgis’s results are entirely con- 
firmatory of those of Stahl. Wahlberg (84), studying Anaptychia and 
Physcia, thought there was no doubt that asci and paraphyses come 
from the same hyphae. For Anaptychia, Baur (5) found later that the 
enveloping hyphae and the paraphyses do not come from the hyphae 
which are directly around the the carpogone, but mostly from hyphae 
above the ascogone. Darbishire (25) describes the origin of the para- 
physis bearing hyphae in Physcia from several cells which are between 
the ascogone and the hyphae on which it is borne, and which in the un- 
fertihzed carpogone are longer and narrower than the ascogone cells. 
Since from these cells only paraphyses are formed, for brevity he de- 
signates this part of the carpogone the “paraphysogone”. Baur (3) had 
described the origin of the paraphyses from this part of the carpogone 
in Collema crispum. He observed that while the more distal ascogone 
cells are plainly perforated, in these basal cells there is no breaking down 
of the cross walls at all. Darbishire observed that the cells of the “para- 
physogone” were only connected by bands of plasma. These basal cells 
of the carpogone are physiologically the same as the single stalk cell of 
the oogonium in the mildews and as the two or three disc-shaped cells 
which make up the stalk of the oogonium in Pyronema. In the mildews 
(Harper), the hyphae which form the wall of the perithecium come 
from the stalk cell of the oogonium, as in Erysiphe (49) and Sphaerotheca 
(47), or from both this and the stalk cell of the antheridium, as in Phyllac- 
tinia (52). In Pyronema, the hyphae which branch to form the para- 
physes come from the stalk cells of the oogonium and from the neigh- 
boring vegetative cells. Harper was not able to make certain whether 
some of them also arise from the stalk cells of the antheridium or not. 
Claussen says that they arise from the hyphae which bear the sexual cells 
