2o8 Alternation of Generations and Ontogeny. 
development of a complicated body, for we know in many animals 
and plants that an elaborate body may be built up from a free 
egg. 
Apart from experiment (a question which will be dealt with 
later) the theory can clearly only be discussed on general con¬ 
siderations, on the grounds of its relative probability as judged by 
developmental processes generally, and especially by those of other 
organisms with a complicated life-cycle. 
One of the chief arguments urged in favour of this view is in the 
nature of a dilemma. We are presented with two possibilities : 
(a), “ that the germ-cells are so different that they necessarily give 
rise to bodies of different structure,” (b), that the two germ-cells 
are alike, but the resultant bodies are different owing to the 
different conditions of early development. Dr. Lang accepts the 
second view, but to the writer it seems that the first (with the 
omission of the word “ necessarily)” should be accepted as more 
probable. 
There do not appear to be any serious difficulties in conceiving 
the egg and spore as different, in believing that one has received 
from the plant which bore it a tendency to become a sporophyte, 
the other, a tendency to become a gametophyte. The orderly 
unfolding of the root, stem, leaf and flower in the development of 
the ordinary plant is explained mainly by internal factors, such as 
growth correlation and the influence of one stage upon one another. 
It would seem then a simple extension of this view to apply it to 
the whole life-cycle of a given organism however complicated, and 
to consider the various stages as united together by a cyclical coyre- 
lation , one stage influencing the development of the other. It 
is quite clear that different types of germ-cells of an organism, 
because they are freed from connexion with other cells, are not 
necessarily in the same state ; one has only to consider the case of 
zoospores and gametes. 
It can easily be shown that the germ-cells in many forms 
are just as dependent on their position in the life-cycle for the 
way they shall develop, as are the cells of the primordium of a leaf 
on their relation to the general body. A single example will make 
this clear. If we consider Puccinia graminis we have no less than 
four kinds of germ-cells—teleutospore, sporidia, aecidiospores, 
uredospores. If all these four be placed on a barberry-leaf 
in moist air the first will form, not an ordinary germ-tube, but a 
special promycelium; the other three will form germ tubes, but 
