Alternation of Generations and Ontogeny. 207 
ALTERNATION OF GENERATIONS AND ONTOGENY, 
By V. H. Blackman, Sc.D. 
(.Professor of Botany at the University of Leeds). 
N the January number of this journal Dr. Lang published a 
very interesting suggestion concerning the relation of the two 
generations in the Archegoniatae, and his views were discussed at 
the Linnean Society, as reported in the March number of The 
New Phytologist (p. 104). At that discussion most of the 
speakers were concerned with the current theories of alternation 
and their relation to the new views, while little attention was paid 
to the question of the probability of the theory proposed. The 
views of one who was not present at the Linnean Society on that 
occasion, and who finds very great difficulty in accepting Dr. Lang’s 
theory of ontogeny may perhaps be contributed to the discussion 
in this form. 
It is not proposed to deal with the thorny question of the 
mode of origin of the two generations, but almost solely with the 
question of the physiological reason for the difference of gameto- 
phyte and sporophyte. 
In Dr. Lang’s view the differences in the two generations (in, 
for example, homosporous ferns) are the result of external con¬ 
ditions. The egg and spore when formed are conceived to he in a 
perfectly neutral condition, without any tendency to form either 
gametophyte or sporophyte. As a result, however, of the difference 
of conditions in which the two cells start their development—the 
spore free on damp earth and the egg protected and nourished 
in the archegonium—-the product of the two is very markedly 
different; one becomes the small prothallus, the other the large 
differentiated sporophyte. 
Such a theory is very simple, and, if it could be accepted, 
would give a very clear idea of the relations of the two generations. 
The differences between the two are, however, so great that it is 
difficult to believe that they are solely the result of differences in the 
conditions of early development. One would also expect that what¬ 
ever the origin of the two generations, the cyclic processes of alter¬ 
nation would by now have become impressed, at least in part, on 
the protoplasmic mechanism of development. Further, a protected 
and highly nourished condition is clearly not necessary for the 
