Alternation of Generations based on Ontogeny. 3 
widely recognised. The references to the origin of alternation of 
generations by Schenck 1 and by Goebel 2 may be specially mentioned, 
since some of the views elaborated below are clearly stated by 
these investigators, though not developed in detail. 
It is remarkable that physiological works, even when dealing 
expressly with the causes of specific shape and the nature of 
ontogenetic development, have given little consideration to the 
special problems raised by the life-history of most plants consisting 
of two alternating generations. This important aspect of the 
question of the transmission of characters and the explanation of 
ontogeny has doubtless not been emphasised because the develop¬ 
ment of the flowering plant can be experimentally treated as if it 
were as straightforward as that of a higher animal. In reality 
the alternation requires to be taken into consideration here, just 
as it more obviously does in the case of the Fern or the Bryophyte. 
The point of view which gives special weight to the comparison 
of the two generations in the same plant, or limited group of 
plants, may be contrasted as ontogenetic with the comparisons 
between the sporophyte of the vascular plants and the gametophyte 
of other and very distantly related groups, which form the basis 
of the hypothesis of Lignier, and of others already mentioned. 
These have been classed above with the purely phylogenetic 
theories. The importance of concentrating attention upon the 
ontogenetic aspect appears to me to lie in the possibility that it 
leads to a working hypothesis which will supersede the antithetic 
and homologous theories as at present stated, and be fruitful 
in suggesting new lines of investigation into the subject. Perhaps 
the most important of these lines are those on which the theory 
may to a certain extent be experimentally tested. 
With this very general reference to the work of other investi¬ 
gators I propose to consider briefly what appear to me the most 
important facts bearing on alternation and to follow out what is 
implied by some assumptions that we are forced to make. On these 
I shall venture to outline a working hypothesis, based primarily on 
the facts of the ontogeny, as to the origin of the alternation in 
Bryophyta and Pteridophyta. So far as I know the views to be 
expressed differ as a whole from any that have hitherto been 
stated, but it should be pointed out that practically all the facts 
1 Ueber die Phylogenie der Archegoniaten und der Characeen. 
Engler’s Botan. Jahrbuch. Bd. XLII., Heft I., 1908. 
2 Einleitung in die Experimentelle Morphologie der Pflanzen, 
p. 199, &c, 
