TRANSACTIONS OF SECTION K. 997 
On this view, tke sporophyte first appeared as a mere group of spores formed 
by the division of the fertilised ovum. Consequently the inference is drawn that 
ail the vegetative parts of the sporophyte have arisen by the ‘sterilisation of 
potentially sporogenous tissue.’ That is to say, there was nothing but a mass of 
spores to start with, so whatever other tissues and organs the sporophyte may form 
must be derived from the conversion of spore-forming cells into vegetative cells. 
Professor Bower has worked out this view most thoroughly, and as the result he 
is not only giving us the most complete account of the development of sporangia 
which we have ever had, but he has also done much to clear up our ideas, and to 
show us what the course of evolution ought to have been if the assumptions 
required by the antithetic theory were justified. 
Without entering into any detailed criticism of this important contribution to 
morphology, which is still in progress, I wish to point that we are not, after all, 
bound to accept the assumption on which the theory rests. There is another view 
in the field, for which, in my opinion, much is to be said. The antithetic theory is 
receiving a most severe test at the friendly hands of its chief advocate. Should it 
break down under the strain we need not despair, for another hypothesis remains 
which I think quite equally worthy of verification. 
This is the theory of Pringsheim, according to which the two generations are 
homologous one with another, the odphyte corresponding to a sexual individual 
among Thallophytes, the sporophyte to an asexual individual. To quote Prings- 
heim’s own words:! ‘The alternation of generations in mosses is immediately 
related to those phenomena of the succession of free generations in Thallophytes, 
of which the one represents the neutral, the other the sexual plant.’ Further on* 
he illustrates this by saying: ‘The moss sporogonium stands in about the same 
relation to the moss plant as the sporangium-bearing specimens of Saprolegnia 
stand to those which bear odgonia, or as, among the Floridex, the specimens with 
tetraspores are related to those with cystocarps.’ This gets rid of the intercalation 
of a new generation altogether; we only require the modification of the already 
existing sexual and asexual forms of the Thallophytes. 
The sudden appearance of something completely new in the life-history, as 
required by the antithetic theory, has, to my mind, a certain improbability. Ha 
nthilo nihil fit. We are not accustomed in natural history to see brand-new 
structures appearing, like morphological Melchizedeks, without father or mother. 
Nature is conservative, and when a new organ is to be formed it is, as every one 
knows, almost always fashioned out of some pre-existing organ. Hence I feel a 
certain difficulty in accepting the doctrine of the appearance of an intercalated 
sporophyte by a kind of special creation. 
We can have no direct knowledge of the origin of the sporophyte in the Bryo- 
hyta themselves, for the stages, whatever they may have been, are hopelessly lost. 
n some of the Algze, however, we find what most botanists recognise,as at least a 
parallel development, even if not phylogenetically identical. In Gidogonium, for 
example, the odspore does not at once germinate into a new plant, but divides up 
into four active zoospores, which swim about and then germinate. In Coleochete 
the odspore actually becomes partitioned up by cell-walls into a little mass of 
tissue, each cell of which then gives rise to a zoospore. 
In both these genera (and many more might be added) the cell-formation in 
the germinating odspore has heen generally regarded as representing the formation 
of a rudimentary sporophyte generation. If we are to apply the antithetic theory 
of alternation to these cases, we must assume that the zoospores produced on ger- 
mination are a new formation, intercalated at this point of the life-cycle. But is 
this assumption borne out by the facts? I think not. In reality nothing new is 
intercalated at all. The ‘ zoospores’ formed from the odspore on germination are 
identical with the so-called ‘ zoogonidia,’ formed on the ordinary vegetative plant at 
all stages of its growth. 
In science, as in every subject, we too easily become the slaves of language. 
1 Gesammelte Abhandlungen, II. p. 370. 2 Ibid, p. 371. 
3 See Bower, Antithetic Alternation, p. 361. 
