Origin and Development of the Compositce. i 19 
These few examples serve to illustrate the two sources of the 
involucre in other families. In the one case the involucral members 
are the bracts of the outer florets, e.g., Umbelliferae and some 
Leguminosae; in the other case the involucre is composed of 
purely cauline leaves, e.g., some Leguminosae, Anemone, Nigella 
and Siphocampylus spp. The tendency to form secondary aggrega¬ 
tions of capitula is present in several families in addition to the 
Compositae, and may be illustrated by Xylia Kerrii in the 
Leguminosae (4). 
As the pluriseriate involucre arises either by the progressive 
sterilisation of successive rows of bracts or by the progressive 
aggregation of cauline leaves the primitive involucre is obviously 
the type with a limited number of bracts arranged more or less in 
one row as in the Umbelliferae, with or without a small and 
indefinite number of reduced cauline leaves. 
The difference in origin corresponds very closely with Cassini’s 
“ pdricline ” and “ involucre ’’; and the uniseriate pericline is clearly 
the primitive type with no sterilisation of bracts, while the 
“ involucre ” of a few more or less scattered members is likewise in 
the primitive condition. 
The term “ pericline ” will be used here to indicate the leaf- 
base structures of the involucre which have, or which probably have 
had, florets in their axils. As the term “calyculus ” is in common 
use it will be used here to denote the outer part of the involucre 
which originates from purely cauline leaves. This obviates the 
difficulty of the variation in terminology, duplex involucre, secondary 
involucre, pseudo-involucre, etc., having been used in various 
attempts to distinguish between the two parts of the complete 
involucre (cp. Blake, 2). 
Cassini’s distinction between reduced and foliaceous members 
of the calyculus does not seem to be of much importance, when the 
mobile condition of the vegetative parts, especially in a dense 
inflorescence, is recognised. The homology of these reduced cauline 
leaves is obvious in such cases as Cavea (IV, 78, Pl.V) where 
reduction proceeds simultaneously with the progressive aggregation 
of the cauline leaves, and also in Gynura elliptica (8, PI. 11), Senecio 
crepuUformis and S. Peorsonii (11, Figs.8-9). The not infrequent 
occurrence of apostasis in the calyculus is due to the elongation of 
nodes which are normally suppressed. 
As the complete involucre of the Compositae usually includes 
both calyculus and pericline it seems that both cauline leaves and 
floral bracts contribute to this part of the capitulum. 
