ANDREAEALES 275 
progressive from within, which has 
extended in Sphagnum, as in Anthoceros, 
to the whole product of the endothecium, 
while in both the archesporium takes its 
origin wholly from the amphithecium. A 
key to this difference of Sphagnum from 
all other Mosses may be found in Woto- 
thylas, in which the sporogenous cells 
may arise from both sources, the centri- 
fugal progress of sterilisation being less 
completely carried out there than in 
Anthoceros. In both cases the difference 
appears referable to the degree of centri- 
fugal sterilisation in a body in which the 
spore-production was originally central. 
Thus the condition of Sphagnum is in 
this respect the most advanced in the 
Mosses, as that of <Azthoceros is among 
the Liverworts. As regards decentrali- 
sation of the fertile tissue the rest of the 
Mosses will be seen to correspond to 
the less extreme types of the Hepatics, 
while the columella-less sporogonia of 
Notothylas link together the two degrees 
of decentralisation. 
B. ANDREAEALES. 
The mature sporogonium of Andreaea 
offers analogies with that of Sphagnum 
in its form, with its short seta and large 
foot, the whole being borne up on an 
elongated pseudopodium; it also corre- 
sponds in the fact that the columella is 
interrupted at the apex, and covered by 
the archesporium which forms a complete 
dome (Fig. 133); but it differs in the 
dehiscence when mature by longitudinal 
slits. 
The segmentation of the zygote corre- 
sponds to that of other Mosses rather 
than to that of the Hepatics, for after 
the appearance of the transverse basal 
Th 
Ww --- 
Ld 7 
pehaue 
i 
Cy 
toh tht 
§ 
Median longitudinal section of sporogonium 
of Andreaca rupestris, at the time of division 
of the archesporium. #=pseudopodium ; /= 
foot; v=vaginula; /=neck ; c=columella ; 
w=wall of sporogoniui ; e=epidermis ; s= 
spore sac; ¢=archesporial cells dividing ; 
y=calyptra; z=neck of archegonium. (After 
Kiihn.) X80. 
wall, the cleavages are oblique, a two-sided initial cell being present (Fig. 
134 A-D); but the number of such segmentations is limited to about a dozen. 
