TRANSACTIONS OF SECTJON K. — PRESIDENTIAL ADDRESS. 725 



Section K.— BOTANY. 

 President of the Section. — Professor F. W. Oliver, D.Sc, F.R.S. 



THURSDA T, A UG UST 2. 

 The President delivered tbe following Address : — 



The Seed, a Chapter in Evolution. 



As the subject of the first portion of my Address I propose to consider the 

 place of the seed in the evolutionary history of plants. The seed-character is 

 the distinctive mark of three great groups of plants — the Pteridosperms, Gymno- 

 sperms (including Cordaitefe), and Angiosperms. Nor will it be seriously ques- 

 tioned that the possession of this organ has given supremacy to seed-bearing 

 plants over groups not thus characterised in a majority of the types of environment 

 where vegetation is able to exist. Exceptions, of course, there are, though few 

 of them are wholly immune from tbe invasion of the Spermophyte. The sort of 

 habitat, for instance, in which Zostera flourishes — sometimes to the exclusion 

 of other forms — is held more as a result of vegetative aggressiveness than iu virtue 

 of any special power still conferred by the seed-habit. 



Our stock of knowledge of those plants which had attained to the seed-bearing 

 condition in a bygone age has undergone some extension during the last few years ; 

 the seed, too, has shed its glamour over other branches of botanical inquiry, 

 so that no serious apology is necessary for its selection as the subject of this 

 morning's discourse. 



It is generally conceded that the primitive vegetation arose in the waters, and 

 that with the parting of the waters and the emerging of land and continents this 

 primitive stock of plants was sufficiently plastic to take advantage of the new 

 conditions, throwing up successive hordes which effected a footing on the land, 

 and in time peopled the whole earth with forms adaptable to the varying habitats 

 and climates as they differentiated. 



Of the character of these primaeval aquatic types no direct information has 

 been vouchsafed. It is a matter of inference that they possessed much in common 

 with the green Algse of to-day, which, living in a biologically stable medium, are 

 commonly regarded as their nearest representatives. Be that as it may, the com- 

 plexity of the life-history of existing Algae and the frequent presence of neutral 

 generations seem significant of the capacity of their progenitors to originate forms 

 with sporophytes adapted to terrestrial conditions. 



In our Liverworts and Mosses on the one hand and the Feres and their allies on 

 the other, two divergent evolutionary lines are represented, both fitted to existence 

 upon land surfaces, but handicapped by the retention of a non- terrestrial method 

 of effecting the sexual process. In the Bryophytes the physiological continuity 

 and dependence of the sporophyte upon the gametophyte is preserved throughout, 

 and it never rises above the status of an elaborate spore-capsule ; whilst the gameto- 

 phyte, though often reaching a complex A-egetative differentiation, offering many 

 analogies with the sporophytes of higher plants, is condemned to pigmy dimensions 

 through the incubus of the inherited aquatic mechanism of fertilisation. 



