T H E 
HEW PHYTOLOGIST. 
Vol. X, No. 4. 
April, 1911. 
[Published May 10th] . 
FLORAL EVOLUTION; WITH PARTICULAR REFERENCE 
TO THE SYMPETALOUS DICOTYLEDONS. 
By H. F. Wernham. 
II. The Archichlamyde.e, and their Phylogenetic 
Relations to the Sympetal^e. 
I T is a remarkable fact that, whereas the flowers of barely 20% of 
the total number of species of Archichlamydeae have stamens 
equal in number to, or less than, the corolla segments, an isomerous 
or oligomerous androecium characterizes nearly 95% of the species 
of Sympetalae. Only about 18%, again, of the Archichlamydeae have 
a pistil composed of two syncarpous carpels or, in some rare cases, 
of one only; in the Sympetalse, on the other hand, fully 75% of 
the species have flowers with a bicarpellary gynaecium. 
The natural conclusion to he drawn from these facts is that 
the progressive tendency to economy of production, observable at 
work, so to speak, in the Archichlamydeae, has reached a high degree 
of realization in the Sympetalae. In accordance with the principles 
formulated in the first chapter, we shall consequently expect to find, 
in the latter group, the second fundamental principle, that of pro¬ 
gressive adaptation to insect visits, the more active. This is actually 
the case; a corolla-tube, of course, is almost invariably present in 
the Sympetalze; aggregation into dense inflorescences is the 
principal feature of the Composite, which comprise over 27% of the 
total number of sympetalous species, and, indeed, over 10% of the 
sum total of flowering plant-species. Zygomorphy, moreover, 
occurs in quite 45% of the Sympetalse, as against barely 15% in the 
case of Archichlamydeae. 
