H. F. Wernham. 
Evolutionary Genealogy. 
o 
84 
The terms “ monophyletic ” and “ polyphyletic ” are relative 
only; traced further down, our seven “sympetalous” lines converge 
upon the Ranalian Common Ancestor. Any polyphyletic group, in 
fact, is conceivable as monophyletic if its history he traced with 
sufficient remoteness. It is important that we should examine this 
statement in some detail. 
Certain groups of considerable importance and extent have not 
made their appearance in our story of the Sympetalae; such are the 
bulk of the Monochlamydee or Incomplete of Bentham and 
Hooker. In this group these authors included those Dicotyledons 
in which the flower has only one perianth-whorl; and, to say the 
least of it at this juncture, the separation of Incomplete from 
Polypetalae seems to be as justifiable as the separation of Sympetalae 
from Archichlamydeae. 
In an ideal system of classification, based, that is to say, 
entirely upon relationships, it may be that there should be no two- 
or three-fold division of the Dicotyledons. We have arrived at the 
conclusion that Sympetalae, at any rate, should not exist as a 
separate group. If this be so, however, all the Dicotyledons must 
be referable to the branches of a single tree of affinities, with a 
single ancestor at its base. The latter must, moreover, be itself a 
Dicotyledon ; otherwise the Dicotyledons will lie upon two or more 
separate trees connected in descent only at a point below, i.e., 
preceding, the evolution of the Dicotyledons. 
The accompanying diagram may serve to make this important 
point clearer. The ramifying lines represent that portion of the 
evolutionary tree upon which lie all the Angiosperms, ultimately 
descended, we suppose, from a pro-angiospermous ancestor A. 
The lines X, Y, Z, represent surfaces, the whole branch-system 
occupying all directions in space as may be necessary ; X marks 
the boundary between pro-angiosperms and angiosperms, all the 
latter lying above it. Similarly all the existing and fossil Mono¬ 
cotyledons and Dicotyledons are supposed to lie above Y; so that 
the space between X and Y is occupied by Angiosperms prior 
in descent to the separation of Monocotyledons from Dicotyle¬ 
dons. Certain of the Rauales, e.g., some of the Nymphaeceae, 
may not impossibly lie in this region. M and D represent the res¬ 
pective ancestors of the two groups, connected, we suppose, only 
through a pro-angiospermous ancestor A. The portion of the tree 
which we have investigated in these papers is enclosed in the circle 
