676 CONCLUSION 
suspensor, and with the apex directed to the archegonial neck. A similar 
probability may be recognised in the Ophioglossales, and Aotr. obliguum 
may be held to illustrate the more primitive embryogeny; and: it shows 
also that an awkward curvature during development is entailed on the 
young embryo (Fig. 264): the type common for the rest, without suspensor, 
and with the apex directed to the archegonial neck would be the derivative, 
and in them the awkward curvature is avoided. As regards other phyla, such 
as the Equisetales and Filicales, where a suspensor is absent, the question 
must remain open; but there is nothing apparently to oppose the view 
that they also may have sprung from a stock with a suspensor, and 
that, as suggested for Jsce¢es, and for most of the Ophioglossales, they 
also may have broken away from a development which had ceased to be 
practically useful. The evidence from the Ferns, such as it is, indicates 
a probable progressive reduction of the prothallus on passing from the 
Eusporangiate to Leptosporangiate types: this would accord with a 
general opinion that the primitive Pteridophyte prothallus was generally 
a massive structure, and the primitive embryo which it nursed of the 
type with a suspensor. 
A comparison of the spindle-like embryonic axis of the Pterido- 
phytes which these observations have disclosed with the young sporo- 
gonium of Bryophytes, and especially of some of the Jungermanniaceae, 
is inevitable: it would, however, be an error to press this comparison 
closely. In both cases a segmented body of radial symmetry is 
recognised, endowed with growth. But there is no sufficient reason to 
believe that any living sporogonium really prefigures any early Pterido- 
phyte: the similarity may well have had its evolutionary origin along 
distinct phyletic lines, but subject to somewhat similar biological 
requirements. On this point the difference in position of apex and base 
has its interest; while tle suspensor of Pteridophytes points to the neck 
of the archegonium and the apex towards the nutritive prothallus, in 
Bryophytes the apex is towards the neck of the archegonium and the 
foot, or in Jungermanniaceae the basal appendage, grows into the tissue 
of the gametophyte. There would appear to have been an _ essential 
difference of method here: in the one case leading to the direct establish- 
ment of an ephemeral sporophyte, deriving its nourishment from a 
perennating gametophyte, and demanding early dissemination of its spores: 
this is characteristic of the Bryophytes. On the other, the tardy establish- 
ment of a perennating sporophyte deriving its nourishment at first from 
the gametophyte, but eventually achieving a power of self-support, and 
producing its spores relatively late: this is characteristic of the Pterido- 
phytes, and extended with modifications to the whole Vascular Vegetation. 
From the above pages it will appear that the evidence to be drawn 
from comparative embryology as bearing on the morphology of the shoot 
is by no means to be neglected. When the fluctuating characters and 
features of more immediate adaptation are removed, there remains a sub- 
