2 16 Alternation of Generations and Ontogeny. 
which naturally suggest themselves are the transference of one germ¬ 
cell to the natural place of development of the other. It is hardly 
conceivable, however, that the poorly-clad egg-cell will be able 
to withstand the rigorous conditions that suit the well protected 
spore, even if the experiment could be performed ; and the reverse 
experiment is hardly possible. Even if the first experiment were 
successful and the egg developed into a gametophyte, the result 
could hardly be considered as proving that the egg and spore were 
in an exactly similar state. 
Such a sudden change of conditions might easily alter the state 
of the cell and so overcome the original tendency , 1 for as already 
pointed out it cannot be considered as irrevocable. We know that 
a change of conditions may affect the relation of the organs in the 
development of an ordinary plant-body. The case may be mentioned 
of the female Lychnis dioica which, on the attack of a fungus (Ustilago) 
develops anthers, the normally latent male characters being brought 
out. 
How difficult of interpretation are experimental results is shown 
also by Goebel’s observations where under similar conditions he 
obtained from the primary leaves of ferns , 2 not only prothallia and 
sporophytes, but also a new combination of determinants resulting 
in a structure intermediate between a leaf and a prothallium. These 
observations do not lend any support to the view that the external 
factors are primarily concerned in the production of the two body- 
forms, for both were produced under the same conditions, and an 
intermediate one also. Such difficulties of interpretation are only to 
be expected when it is considered how crude such experiments really 
are. The whole range of the obscure life-processes of the plant lie 
between the actual result of the alteration of conditions and the 
phenomena we observe. 
Even if it were shown that the egg and spore are exactly 
similar, and that different external conditions lead to the appearance 
of sporophytic and gametophytic characters respectively, the result 
could bear the interpretation that external conditions serve 
as orientating stimuli to the plant and so decide the question 
of which determinants shall develop. The two sets of determinants 
(with no doubt some in common) might still have been acquired 
by two separate lines of evolution (as has been suggested for the 
1 Such vague phraseology would seem unavoidable while the cell- 
factors in development are so complex and imperfectly known. 
What is clear is that the egg and spore contain all the 
characters of the organism so that under certain conditions 
any or all of the characters may be brought out. 
2 Einleitung in die experimentelle Morphologie der Pflanzen, 
1908, p. 199. 
