i 2 W. H. Lang. 
made long ago by Treub. The peculiarities of the Lycopodiacese 
have also led Lignier to suggest that their leaves are of a different 
nature to those of the Ferns. He distinguishes them as “ phylloides ” 
and compares them with amphigastrial scales of the thallus of his 
hypothetical pro-hepatic type. 
While the particular comparison made by Lignier appears to 
me to he open to serious objections, I am led by the comparison of the 
two generations to a similar conclusion as to the difference between 
the leaves of the Lycopods and the Ferns. I should incline to regard 
the leaves of thesporophyte of the Lycopods, and also the leaves of the 
Equisetales, as corresponding to the assimilating lobes of the 
prothallus in the respective groups. This amounts to regarding both 
these groups as primitively microphyllous, but is not inconsistent 
with branching and the attainment of a considerable size by the 
leaves. The morphology of the two generations in these groups, 
contrasts with that of the prothallus and sporophyte of the Fern. 
The brief general application of the ontogenetic hypothesis of 
alternation to the Vascular Cryptogams, which has been made in the 
last paragraphs, is of course quite provisional, and will require to be 
considered critically, at greater length and in greater detail. It will 
serve to suggest, however, that the broad comparison of sporophyte 
and gametophyte within the same group on these lines points to 
conclusions which agree with the important distinction on anatomical 
grounds of the Lycopsida and Pteropsida and with speculations 
based on other evidence. The hypothesis finds support in the facts 
which present most difficulty on an antithetic or on a monophyletic 
homologous theory. 
Direct evidence on any view of the origin of the alternation of 
generations in archegoniate plants must from the nature of the 
case be slight. It may be claimed for the ontogenetic hypothesis 
advanced above that it brings into prominence the important factor 
of the different conditions of the ontogeny of the two generations 
and that it will lead to work on new lines and is open to 
experimental test. Experiment may not, as has been objected, be 
able “ to reconstruct history,” but it may show whether the two 
generations in the complete life-cycle are the results of equivalent 
germ-cells developing under different conditions, as is here suggested, 
or not. 
