676 CONCLUSION 



suspensor, and with the apex directed to the archegonial neck. A similar 

 probability may be recognised in the Ophioglossales, and Botr. vbliquum 

 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 Isoetes, 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 the 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- 



