Floral Evolution. 
“5 
relatively large and solitary flowers, there is no general tendency to 
this condition in the Archichlamydeae. Like the capitulate inflores¬ 
cence, zygomorphy is not very uncommon in particular and 
phyletically isolated cases from among the Ranales upwards; but 
it does not form a critical character of any synthetic group 
comparable with the Lamiales and Personales of Bentham and 
Hooker—with which we shall have to deal later. 
Zygomorphy occurs in the following groups of Archichlamydeae: 
Proteales (Proteaceae), where it is prevalent; Santalales, 
Aristolochiales, Rhoeadales, Opuntiales,—where it is not uncommon ; 
it characterizes many members of groups D and E of Geraniales, 
and D and E of Sapindales; while examples of zygomorphy are not 
lacking in Ranales, Rosales (notably the Papilionatae tribe of 
Leguminosae), Parietales, and Myrtiflorae. 
All these casies, however, together with the Umbelliferae, amount 
to about 15% of the total number of species of Archichlamydeae. 
(iii.) Fusion , in so far as this tendency subserves the principle 
of progressive adaptation to insect-visits, plays a very inconspicuous 
part among Archichlamydeae. A corolla-tube is, of course, 
characteristically absent; although one or two specialized 
“apetalous” groups, notably the Proteales, the Aristolochiales, the 
Nyctaginaceae, etc., have flowers with a typically gamophyllous 
perianth. In a few rare cases, too, a gamopetalous corolla occurs 
among the higher heterochlamydeous forms ; but in the majority of 
these it would appear probable that the cohesion occurs some time 
after the initial stages in the development of separate petals 
have been passed. It may be suggested, perhaps, that a truly 
sympetalous corolla would seem to be one in which the component 
petals are united, if not from the outset of development, then at 
a very early stage. One result of such a circumstance would be 
that a pseudo-sympetalous corolla, if we may so express it, would 
conceivably betray itself by the absence of close cohesion at the 
base: and this is actually the case in Correa, for example, an 
Australian Rutaceous plant cultivated occasionally in conservatories. 
In some species of Correa, moreover, the corolla-tube breaks up 
after maturity into separate petals. 
A tendency to tube-formation by cohesion of the staminal 
filaments is clearly distinguishable in the Geraniales ; for in most 
of the natural orders of this cohort the filaments are more or less 
united, at least at the base. This tendency reaches its highest 
expression in the Meliaceae, a large tropical and sub-tropical order, 
