14 THE AMERICAN NATURALIST. (VoL. XXXIX. 
missed this question with the following brief statement, ** That 
the Monocotyledons and Dicotyledons have a common ancestry 
there is no reason to doubt. One would hardly suppose that 
the similar complicated cytological phenomena of embryo-sac 
development and endosperm formation were simply parallelisms 
in two groups of different phylogenetic origin.” Later, how- 
ever, Balfour (:o1) in discussing the phylogeny of the angio- 
sperms, said, * Were I to maintain an opinion it would be that 
the two classes have arisen on separate lines of descent. The 
embryo characters as well as those of the epicotyl can, I think, 
be shown to be fundamentally different and to afford no basis 
for an assumed phyletic connection." 
Since Balfour, Coulter and Chamberlain (:03) have written 
on the same subject as follows: * The first phase of the prob- 
lem has to do with the common or independent origin of the 
Monocotyledons and Dicotyledons. It has been assumed gen- 
erally that the two groups are monophyletic. The chief argu- 
ment, and in fact the only morphological one for the monophyletic 
theory, lies in the great uniformity of the peculiar development 
of both male and female gametophytes. It is argued that the 
independent origin of such exact details of development and 
structure is inconceivable, and this argument has been reén- 
forced recently by the discovery in both groups of the peculiar 
phenomenon called. ‘double fertilization. The argument is cer- 
tainly a very strong one, and yet there are rebutting proposi- 
tions. Even such similarity in structure may be the natural 
outcome of the changes that resulted in the evolution of seeds, 
and these are now generally believed to have appeared in inde- 
pendent lines. Again, the fundamental differences in the devel- 
opment of the embryos of the two groups are hard to reconcile 
upon the theory of monophyletic origin. Add to this the funda- 
mental differences in the structure of the stem and in the 
character of its vascular bundles, and the derivation of one group 
from the other seems more inconceivabie than the derivation of 
the Dicotyledons from the Gymnosperms. Still another argu- | 
ment against the monophyletic theory is furnished by the histori- 
cal testimony. The Proangiosperms of the Lower Cretaceous, 
so far as known, appeared associated with undoubted Mono- 
