18 BOTANICAL GAZETTE [JANUARY 
monocotyledons and anomalous dicotyledons, HeNsLow’s conclu- 
sion that the former have been derived from the latter as a re- 
sponse to the same factors that determined the geophilous habit 
is reasonable, at least, as a working hypothesis. Failure to recog- 
nize the fact, however, that geophily may express itself variously 
has sometimes led to disagreement in theories where none actually 
exists. This appears especially in discussions of the origin of the 
monocotyledonous from the dicotyledonous habit, it being held 
that monocotyledony has arisen in only one way. There are at 
least three plausible theories concerning the method by which this 
may have occurred: first, by suppression of one of two cotyledons; 
next, by fusion of two cotyledons; and, finally, by a division of 
labor between two cotyledons. Now since we find a difference in 
the behavior of the cotyledons in certain anomalous dicotyledons, 
it is entirely probable that the same thing has happened in the 
origin of monocotyledons from dicotyledons, so much the more 
so if there is more than one monocotyledonous branch from the 
primitive dicotyledonous stock. 
While, as has been shown, the most generally accepted view is 
that angiosperms are. monophyletic we must also remember the 
possibility of a diphyletic origin. CouLrer (6) has expressed his 
view on this point as follows: ‘‘In our judgment the evidence is 
strongly in favor of the independent origin of the two groups, 
which have attained practically the same advancement in the 
essential morphological structures, but are very diverse in their 
more superficial features. Their great distinctness now indicates 
either that they were always distinct or that they originated from 
forms that were really proangiosperms and neither monocotyledons 
nor dicotyledons.” Those who hold this view will have to explain 
more satisfactorily than has been done the similarity between 
monocotyledons and dicotyledons in gametophytic development 
and in seedling structure; the general similarity between mono- 
cotyledons and anomalous dicotyledons; and the evidence that 
primitive angiosperms possessed a cambium and were dicotyle- 
donous. The monophyletic theory has been strongly reinforced 
in recent years and the writer finds it more acceptable than the 
diphyletic, but more evidence is needed before it can be unreservedly 
accepted. 
