()6 PROCEEDINGS OF THE 



PKESIDENTIAL ADDRESS, 1910. 



I PROPOSE to take as the subject of my Address this year " Some 

 Modern Ideas on the Course of Evolution of Plants " — an extensive 

 field, no doubt, whicl) it will only be possible to sketch in the 

 merest outline on an occasion like this. The bearing of recent 

 investigations in Fossil Botauy on the problem will come in for a 

 good deal of attention, but obviously it is impossible to limit oneself 

 to this point of view. 



I do not intend, however, to enter with any freedom upon the 

 regions of pure theory, in which we must include the great question 

 of the origin of the Alternation of Generations, characteristic of 

 the higher plants. 



Dr. Lang, it is true, in the remarkable paper which we discussed 

 in February 1909, held out hopes of putting this question on an 

 experimental basis ; it will be extremely interesting to see what 

 comes of this suggestion when practically tested, but I think that 

 much will always remain hypothetical. As Dr. Lang himself 

 recognized, we can hardly hope to reconstruct the conditions under 

 which the sexual and asexual phases first became differentiated, a 

 process which must have taken place ages before the date of our 

 earliest fossil records. 



I may venture, however, to state my conviction that the position 

 of this question, so clearly put before us on the occasion referred 

 to, IS now far more hopeful and stimulating to research than it 

 was a few years back. Dr. Lang said : — " If this ontogenetic 

 view is correct, we should be justified in seeking for correspondence 

 in the vegetative organs, and possibly also in the reproductive 

 organs, between two individuals of the same life-cycle. These 

 correspondences — though between haploid and diploid individuals 

 — I should term homologies, since they may amount to practical 

 identity when the conditions of development are exactly the 

 same " *. 



It is not very long since the idea of any homology between the 

 sexual and asexual generations would have been scouted by our 

 more orthodox morphologists ; even the heterodox would have 

 hesitated to back their opinions so far as to seek for detailed 

 correspondence. The old antithetic theory not only set up an 

 impassable barrier between the two generations, it also shut off 

 the vascular plants absolutely from everything below them. The 

 sporophyte, i. e. the plant itself, was assumed to be a new inter- 

 i-alation in the life-history, and could therefore never be compared 

 with the plant in Thallophytes, which was supposed to belouo- 

 to the other generation. jVow all this is changed — the Alga 

 Dictyota has given the clue, for it shows us how the two 

 alternating generations, the sexual and asexual, may be exactly 



* Discussion on "Alternation of G-enerations," ' New Phytoloeist," vol viii 

 1909, p. 106. ■ ' 



