Floral Evolution. 
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and all the Sympetalae lie above the surface Z. Now we have called 
the Sympetalae polyphyletic because the single ancestry, R, to 
which their evolutionary lines can all be traced does not itself 
lie above Z,—in other words, because they have not a single 
sympetalous ancestry. 
Diagram shewing possible lines of descent of the Angiospermae from a 
proangiospermous ancestor, A. M, ancestor of the Monocotyledons, D, of the 
Dicotyledons. The Sympetalae and their archichlamydeous ancestry are 
included in the circle, diverging from the Ranalian Common Ancestor, R. 
The lines are supposed to occupy all directions in space as may be necessary. 
Similarly, both the Archichlamydeae and the Monocotyledons 
may be, and probably are, polyphyletic in the same sense ; they are 
so represented in the diagram. Our present concern is with the 
former group. VVe have examined one evolutionary branch-system 
of the Dicotyledons, namely, that which has developed, under 
the several tendencies which we have attempted to trace, from an 
ancestor, R, of the ranalian type, with indefiniteness in all the floral 
parts, and an elongated floral axis. This explains our meaning when 
