242 SECTIONAL ADDRESSES. 



and Algse, are undoubtedly brought nearer together by the Rhynie dis- 

 coveries ; and I may be pardoned for re-quoting from him a passage of 

 my own (^.c, p. 205) : ' Long ago it was remarked that the widest gap in 

 the sequence of plants was that between the Bryophytes and the Pterido- 

 phytes. It is within this gap that the newly discovered fossils take their 

 natural place, acting as synthetic links, and drawing together more closely 

 the whole sequence of land-living, sporangium-bearing plants.' Under 

 the influence of these and other late discoveries the Bryophyta are coming 

 into their own. Not only has the problematical Sporogonites been 

 described by Halle from the Devonian rocks, but undoubted Liverworts 

 of the Carboniferous Period have been disclosed by the refined methods 

 of Walton. These events coincide with the advent of the Psilophy tales, 

 the most sporogonium-like of all vascular sporophytes. It seems there 

 may be a natural place for Anthoceros at last, as Campbell tells us. 



The effect of the establishment of the Rhyniaceous type on the com- 

 parison of the parts of the sporophyte is important ; in particular the 

 question of the origin of the root and leaf may be canvassed afresh. We 

 see a class of early rootless, land-living sporophytes, sharing this feature 

 with the Psilotales, and we may reasonably hold them to represent a 

 primitive type. On the other hand, we see in all Pteridophyte embryos 

 which have a suspensor that the root, often late in appearance, is a lateral 

 appendage on the embryonic spindle. Moreover, the root arises as an 

 exogenous growth in Phylloglossum, and in certain species of ZycoyotiiMm, as 

 do also the enigmatical rhizophores of Selaginella. Provisionally, then, we 

 may conclude that the root is a late addition to the plant-body in descent, 

 and that it was in the first instance some form of exogenous branch at the 

 base of the primitive sporophyte, such as is seen in the Psilotacese and in 

 Asteroxylon. 



Much greater interest and more consecutive reasoning centres on the 

 question of the foliar developments of vascular sporophytes. Studies on 

 ' Leaf -Architecture ' and passages dealing with that subject in my book 

 on Ferns, vol. i, have shown that, by inductive comparison based on an 

 analysis of plants now living, we may arrive at a theoretical origin of 

 leaves of the Fern-type from a dichotomously branching system ; and 

 already in 1884, long before the discovery of the Psilophytales, this con- 

 ception had been tentatively extended to include the axis as well, though 

 the material facts such as we now possess were not then in evidence. It 

 was also concluded from comparison of living plants that the sporangia 

 were originally distal on the branches. Thus the Psilophytales supplied 

 m actual fact a sub-aerial type already contemplated as a result of inductive 

 argument. If this origin of a Fern-shoot by sympodial development from 

 a dichotomous branch system, such as that of the Rhynie fossils, be true, 

 there would be no need to draw upon supposititious ' Algae of the trans- 

 migration ' to explain the origin of leaves of the Fern-type, for sub-aerial 

 plants would be seen to have originated such leaves for themselves. Any 

 similarities between Algae and Ferns in respect of foliar appendages would 

 appear only as interesting facts of homoplasy. 



This does not, however, exhaust thejquestion of foliar origin. Such 

 plants as Thursophyton and Asteroxylon, as well as the living Psilotaceae, 

 present features which suggest a second type of foliar appendage. Lignier 



