ALGAE: AND BRYOPHYTA 661 
origin falls in readily with antithetic theory; under which it ‘would: beheld to 
be a primitive, not an acquired condition.. Moreover, it accords with the 
relatively simple form and structure of the sporogonium when mature! 
this simplicity has made the recognition of the part’ played by. sterilisation 
easier in the Bryophytes than it is in plants where continued embmogeny 
leads to a more complex state. 
But the details of this primary embryogeny are carried out differently 
in Mosses and in Liverworts: in the former, after the first division which 
separates the hypobasal cell, apical growth appears in-the epibasal hemis- 
phere with regular segmentation of a two-sided initial cell: in the latter 
the segmentation in the epibasal hemisphere is not localised apically, but 
after division into octants the ‘growth is intercalary. Both of these types, 
so distinct in their details of segmentation, present points of interest for 
comparison with the more complex embryogeny of Pteridophytes: but the 
analogies offered by the Liverworts are the more instructive. In some of 
them (Ricciaceae) there. is. no distinction of apex and base: it may be a 
question whether this absence of polarity is primitive or acquired. In 
others (Marchantiaceae) there is definite polarity, the whole hypobasal 
hemisphere serving functionally as a foot. and seta, while the epibasal is 
‘ reproductive. In others again (Jungermanniaceae) the hypobasal hemis- 
phere develops into a unicellular appendage of small size; the epibasal 
hemisphere after octant division. undergoes intercalary growth, with repeated 
transverse segmentation: the seta is derived from the lower tiers of cells 
thus produced, and it may be only the uppermost tier that remains fertile 
(Figs. 124, 125). The interest here lies in the. deferring of the propagative 
function, as compared with the: previous cases: the part which is in them 
an absorptive seta is here a small body, with probably a minor or 
temporary function, while the lower part of the epibasal region, which is 
elsewhere propagative, takes up the duty of the hypobasal. The propa- 
gative function is relegated to the apical tier, and thus, on a basis of com- 
parison along the Liverworts, an example is established of that process of 
deferring of the event of spore-production which is an essential feature in 
the theory here put forward. A somewhat similar process has been traced 
in the Mosses; and in the Pteridophytes there is reason to believe that it 
has been very prevalent. The presence of such evidence from phyla which 
have probably been distinct from one another at least in the later phases 
of descent, illustrates what is believed to have been a progressive 
development which owes its prevalence to the fact that it was dictated 
by biological advantage. 
The similarity of the small hypobasal appendage in the Jungermanniaceae 
(Fig. 125) to the suspensor in certain Pteridophytes is a further point 
for comparison ; but it is doubtful whether this is in reality anything more 
than a very distant analogy. In either case the body in question represents 
‘a part of the zygote which takes no active part in the further embryonic 
development: both owe their origin to a form of meroblastic segmentation. 
