Campanulatce. 303 
must be regarded as due to converging development. The main 
lines of floral evolution are limited and few in number, and we see 
them recurring again and again in different circles of affinity; this 
is admirably illustrated in the subsequent genealogy of the Infer®. 
From both the campanal and the rubialian stocks two main 
branches arise; each of these branches leads to zygomorphy of 
one or other of the two types suggested in our opening chapter and 
frequently illustrated since. Thus, zygomorphy induced in the indi¬ 
vidual flower, i.e, apart from aggregation, produced the Lobelioi- 
de® and Goodeniacete from the Campanal Stock, and the Dipsa- 
calian from the Rubialian Stock. Aggregation of florets, with con¬ 
sequent zygomorphy, produced Composite from the Ccampanal 
Stock, and Dipsacaseae from the Dipsacalian Stock. An evolu¬ 
tionary process similar to the last-named, hut on a much smaller 
scale, produced Brunoniaceae from Goodeniaceae. The branchings 
from the Umbellifloral Stock exhibit only one type of zygomorphy, 
namely, that which results from aggregation, as illustrated in Um- 
belliferae. For the rest, the three groups Campanuloideae and 
Calyceraceae; Ruhiaceae and Caprifoliaceae ; Araliaceae and Corna- 
ceae ; represent respectively the nearest living approximations to 
the hypothetical stocks which we have postulated,—the second 
family of each pair reflecting a step in the evolution of the progeny. 
The families which stand highest in the tree, i.e., Umbellifer®, 
Valerianace®, Dipsacaceae, and Compositae, display two or three 
notable points of similarity. In the first place, all are charac¬ 
terised by what we may name the fundamental aggregation of 
flowers into more or less dense inflorescences. This character is 
absent in the broad sense from the ultimate members of the hypo- 
gynous Sympetalae, the higher Tubiflorae, in which zygomorphy of 
the individual flower is the key-note of advance. Some sort of 
relation between the aggregation and the inferior position of the 
ovary is not difficult of conception ; for the relegation of the actively- 
developing female parts of the flowers to a secluded position 
doubtless mitigates any disadvantages of space which might arise 
from the close aggregation, at the same time discharging an 
important protective function. Again, the reduction of the ovules 
to a single one per loculus, which characterizes all the four familes 
just named, is of clear advantage in the same connection, especially 
when viewed from the aspect of seed-dispersal. The pappose calyx 
of Compositae and Valerianaceae is readily conceived as advan¬ 
tageous in operating to release the inferior fruit quickly from a 
