T 94 
Farmer and Digby. — Studies in Apospory and 
In fact, these two processes— -sexuality and meiosis — are knit together 
by the closest physiological ties. They stand each to each in a very 
definite relationship of a causal nature. But there exist no a priori grounds 
for assuming any such necessary connexion between either of them and 
any other features or phases in the life-history, however important these 
may be in themselves. The matter becomes one for independent inquiry, 
in the midst of which it should not be forgotten that post hoc is not the 
same thing as propter hoc. Meiosis may well be found to concur with certain 
events or stages in particular life-histories without any assumption as to the 
existence of any essential or necessary relation being in any way justified. 
The fact that meiosis long anteceded the appearance of the Archegoniatae 
might indicate that the hypothesis as to its necessary relation with in- 
dividual parts of the life-history in these plants requires to be tested 
by a comparison with other groups before it can be admitted. But such 
a comparison with forms outside the archegoniate series at once shows that 
the fundamental assumption underlying the hypothesis is not of general 
application, nor indeed is it universally true even within the series itself. 
Meiosis occurs in all the groups (except perhaps the very lowest, in which 
sexuality is not known), but it does not recur at corresponding periods 
in all alike. Thus, to take the first example of Fucus, the meiotic phase 
involves the two first nuclear divisions in the oogonium, whilst the last 
is a post-meiotic division, and results in the formation of the (potentially 
eight) oospheres. But no one probably would seriously attempt to 
homologize the product of the first two divisions of the Fucus oogonium 
with the spores of a Fern, and to conclude that, the final division in the 
oogonium morphologically represented the prothallium reduced to a mere 
oosphere. The Dictyotaceae present some features of difficulty, but these 
are more apparent, perhaps, than real. Williams has shown that the plants 
bearing sexual organs are made up of postmeiotic cells, the plants that 
issue from the zygote, on the other hand, are premeiotic, meiosis regularly 
occurring during the formation of the tetraspores. Dictyota is far removed 
from the Archegoniatae, and it is not sound morphology to attempt to drag 
into homologous series groups which have had a different phylogenetic 
development. At present, moreover, we are not fully in possession of 
the facts respecting Dictyota , but even if it should ultimately turn out 
that there is a regular alternation between a tetrasporic and a sexual 
generation, the question as to the nature of the alternation itself is one 
which will have to be settled on its own merits, and not by an appeal 
to a widely diverse group such as the Archegoniatae. What we shall 
require to know is, whether there is any evidence to show that within that 
algal group there has been built up from the zygote a cell-colony which, 
from a condition of a parasitic embryo, has achieved independence as 
an asexual spore-bearing individual. It is, on the other hand, still quite 
