114 Discussion on “ Alternation of Generations ” 
events during descent, could have given rise to the sporogonium. 
Thus, whether we chose to regard Riccia as a starting point or not, 
most people would admit that the sporogonium in the Bryophyta had 
from the first developed on its own lines, from the zygote : that it 
had not arisen by modification of a pre-existing organisation, but 
had achieved its present complexity as the result of an intercalated 
cellular development, which had from the first been outside the 
track followed by the gametophyte—the latter track being only 
resumed on the germination of the spores. 
As regarded the Vascular Cryptogams, the problem had again to 
be faced, and faced independently of any conclusions at which we 
might arrive respecting the lower forms of plants. Once more the 
matter was one which could only be settled by appeal to historical 
probability, based on comparative morphology. And although the 
evidence might not be so clear as in some of the other phyla, the 
speaker was led to adhere to the antithetic theory, because it 
appeared to be that most easily reconcilable with the facts as we 
knew them. It was difficult to believe that a prothallium ever 
again arose as the direct outcome of the zygote, led a parasitic life 
upon its predecessor, and then evolved an independent existence as 
a “ sporophyte ” with all the potentialities of development which 
we saw realised around us. The initial step, that of parasitism, was 
not one which, so far as we knew, would be likely to lead to such a 
condition. Parasitism in a form already elaborated, tended to effect 
reduction, not amplification, of vegetative parts, and we saw as a 
matter of fact that parasitic dependence on the sporophyte had 
culminated in remarkable reduction in the organisation of the once 
free-living gametophyte. 
Comparisons had been made between similarities existing, 
especially under certain conditions, between the sporophyte and 
gametophyte of ferns and other Vascular Cryptogams. These 
resemblances might, however, be regarded as examples of homoplasy 
rather than of homology. 
Professor F. W. Oliver said that he thought Dr. Lang had in 
his opening address, gone a long way to establish the homologous 
theory on a firmer basis than it ever had before by showing how 
the linked generations might come to have the relations they actually 
had. There was much to be said in support of the view that the 
archegonium originally liberated numerous gametes—as the 
antheridium did still—and that the passage to terrestrial life with 
the concomitant difficulty of launching these bodies, might have led 
to reduction in numbers of the effective gametes, absence of 
dehiscence and retention, in other words, to the evolution of the 
archegonium as they knew it. In the case of the seed-plants they 
had a converse process. So far as any morphological conclusion 
could be regarded with confidence, they might take it that the female 
gametophyte in the seed-plants had become, in process of time, 
retained. The fact that the steps in this process were almost traceable 
and that the results of retention had been, in the case of the 
spermophytes, one of the most striking new departures in the 
evolution of plants, added much force to the suggestion that 
something closely analogous had happened lower down in the scale 
of life. 
A great difficulty in the old antithetic theory had been to 
understand the difference between the Bryophytes and Pteridophytes 
