H. F. Wernham. 
114 
that there is an unmistakeable tendency to economy in production 
of parts, particularly of sporophylls, but less markedly, perhaps, of 
sporangia. 
The question arises, to what extent has the working of this 
principle of economy been accompanied by the compensatory ten¬ 
dency of progressive adaptation to insect-visits ? 
(i.) As regards progressively increasing conspicuousness, there is 
no strong general tendency to floral aggregation such as we find 
realized and expressed in the Compositas. Dense inflorescences, 
close capitula of florets even, are found—and not very un¬ 
commonly—in isolated cases throughout the Archichlamydeae; but 
aggregation does not characterize any relatively large group, save 
one,—the Umbelliflone,—in which the inflorescence unit is typically 
a close umbel, often delimited, like the Composite head, by an 
involucre of bracts. The constancy of this feature in so large a 
group is significant when we couple it with the advanced state of 
its flowers from the point of view of the economy principle—their 
isomerous alternating whorl of stamens, and their bicarpellary 
gynaecium. 
We may remark, moreover, that although the Umbellifloras thus 
stand apart from and ahead of the other groups of Archichlamydeae 
in this character of aggregation, it is not impossible that the efforts, 
so to speak, of the tendency to aggregation by active branching of 
the floral axes, are reflected in those relatively high groups, 1 of 
varying affinity and comprising a large number of species, in which, 
we have suggested, chorisis has occurred in the parts of the individual 
flower, producing indefiniteness in some or all of them. 
(ii.) The general tendency to zygomorphy goes hand in hand 
with the progressive aggregation noticed above, the outer florets of 
the inflorescence tending to bilateral symmetry; this displays itself 
most conspicuously in the increased development of the corolla on 
the outer side, the result being comparable with the development of 
“ray” florets in Compositae; and, as in the latter case, the outer 
florets in certain Umbelliferae may become unisexual. 
As we have already observed, this type of zygomorphy is 
probably the direct result of the mechanical conditions of develop¬ 
ment, growth in the corollas of the outer florets being directed, by 
the stimulus of pressure, towards the exterior. 
As regards the other “ type ” of zygomorphy, J which appears in 
1 Supra, p. 80. 
2 Supra, p. 81. 
