EVOLUTION OF THE INFLORESCENCE. 547 
Possibly the simple (primitive) monochasium might be found to occur in the 
Monocotyledons, as in this group of flowering plants the individual flower 
is accompanied usuaily by a single bracteole, in distinction from the paired 
bracteoles of the Dicotyledons. However, this does not come within the 
scope of this paper, which is concerned with the Dicotyledonous inflorescence 
only. 
If, then, the simple monochasium does not occur, how has the monochasial 
branching arisen in the Dicotyledons? Evidently by a process of reduction. 
If any continuous dichasium be examined, it will be found that one side 
almost invariably develops earlier and the branching is carried further than 
in the other. This is seen even in the Caryophyllaceæ with opposite leaves. 
In alternately arranged leaves, it is obvious that of two adjacent leaves the 
lower will be the first developed, and this may account for the earlier 
peoduction of its axillary floral shoot. At any rate, in a simple dichasium 
arising from alternate leaves, it is the lower of the two lateral flowers which 
blooms first: and in such a dichasium when compound, it is the part of the 
inflorescence which arises from the axil of the lower leaf, that develops 
earlier and branches to a higher degree. 
Opposite leaves in many cases have in all probability originated from 
alternate ones through the suppression of an internode *; consequently, one 
of any pair of leaves will be morphologically the lower, and thus if not 
actually, then phylogenetically, the first of the two to develop. This will 
account for opposite-leaved continuous dichasia behaving in their develop- 
ment like alternate leaved ones. 
By pushing to its farthest limits the unequal development of the two main 
parts of these forking inflorescences, it is easy to see that a continuous mono- 
chasium, in place of a dichasium, would arise. This is apparently how the 
compound monochasium has originated. A striking intermediate stage has 
come to the writer’s notice in the inflorescence of a species of Silene 
(S. pendula). In its earlier branchings it is dichasial, and in its later mono- 
chasial only (fig. 6). Further, the barren b racteole of each pair occurring 
on the monochasial parts of the inflorescence is usually considerably smaller 
than its associate, which bears in its axil the floral shoot. There is tbus a 
tendency for the sterile bracteoles to abort. Also, owing to the successive 
flowers assuming a drooping or lateral position, a false axis (sympodium) 
becomes fairly marked. 
Such an inflorescence strongly suggests that of many Boraginacez. 
Eliminate totally the barren bracteoles, likewise the original terminal flower, 
and accentuate the sympodium, then an inflorescence such as occurs in many 
of the Borage family would result. Further, by pushing the one-sided 
* Groom, P., “ Longitudinal Symmetry in Phanerogamia,” Phil. Trans. Roy. Soc. London, 
vol. 200, B, p. 57, 1909. l 
