EMBRYOGENY OF ‘THE PTERIDOPHYTES 665 
a difference: of initiation of the embryogeny as will serve for a safe 
taxonomic guide. Where a suspensor is formed, the first segment-wall 
(1, 1) divides the zygote, separating the parent-cell of the suspensor from 
what has been styled the embryonic cell (Fig. 355 1.). As the position of 
the first segment-wall in all Pteridophytes where a suspensor occurs is 
approximately at right angles to the axis of the archegonium, the mother- 
cell of the suspensor is directed towards. the archegonial neck, and the 
practical effect of biological moment is.‘that the embryonic cell is thrust 
downwards into the tissue of the nourishing prothallus, While the 
“suspensor is thus recognised as biologically important, it may, on ‘the 
other hand, be regarded as a means of deferring the actual constitution 
Fic. 355. 
Diagrams illustrating the segmentation of embryos. I.=where a suspensor is formed, 
which is cut off by the first wall, 7, /; the suspensor is cross-hatched ; 2, B=basal wall, 
separating the hypobasal hemisphere (dotted) from the epibasal (clear). IT. is the same 
seen from above, x« marking the pole. III.=an embryo where no suspensor is formed, 
and the segmentation resembles that in the embryonic cell where the suspensor is present ; 
the lettering corresponds; x, y indicate the polarity. Each hemisphere divides into 
four by quadrant walls (Q, Q in II.) and octant walls a, 0. 
of the definitive embryo, which is entirely derived from the remaining 
portion of the zygote. The formation of a suspensor is in fact a form of 
meroblastic segmentation, comparable generally, though not in detail, with 
that seen in many Gymnosperms. But a further analogy is to be found, 
as already pointed out, in the sporogonia of the Jungermanniaceae (Fig. 
125): here, however, it is the segment furthest from the neck of the 
archegonium which takes no part in the constitution of the definitive 
sporogonium.! In either case a part of the product of the zygote, 
which has some more or less obvious biological use, may in certain 
forms be set aside from partaking directly in the formation of the definitive 
embryo. : 
Passing now to the embryonic-cell in the Pteridophytes which have 
a suspensor, it has been shown in several well-investigated cases that it 
1ft.is interesting to note that this body is absent from the Marchantiaceae; and the 
inconstancy in the Liverworts may be compared with that of the suspensor in the 
Pteridophyta. 
