546 MR. J. PARKIN ON THE 
branching to some extent is common in early forms of pleiochasia, and that 
one of the steps taken towards racemose inflorescences is shown by the 
suppression of these tertiary floral shoots. In fact, once the axis bearing the 
solitary terminal flower commences to branch producing a dichasium, there 
appear to be two further main tendencies, viz. (1) a tendency to augment the 
number of secondary shoots beyond two, and (2) a tendency to continue 
the floral branching beyond the first stage. These two tendencies may be 
considered in a general way as opposed to each other. We have already 
followed out the evolution of inflorescences due to the first. We have now 
to trace the evolution of inflorescences arising from the second. 
Compound or Continuous Dichasia.—Inflorescences due to the repeated 
branching of the originally simple dichasium are of common occurrence. 
It has already been pointed out that in the primitive cyme (the dichasium), 
flower-buds are often produced in the axils of the paired leaf-structures 
(braeteoles) on the secondary floral axes. If these elongate and expand, 
tertiary axes and flowers are produced respectively, and the paired bracteoles 
on these again may give rise to floral shoots of a still higher order. This 
floral branching may be continued even further. In this way arise the lax 
forking inflorescences (compound or continuous dichasia they may be called) 
characteristic of species of Ranunculus, Potentilla, etc., and specially pro- 
minent and well-developed in the family Caryophyllaeez. In Ranunculus 
acris and R. aconitifolius, flowers to the fifth degree may be produced. In 
some of the Caryophyllacew the floral branching may be carried still further, 
as, for example, in Gypsophila. 
Modifications of these lax repeated dichasia may be brought about through 
internodal compression or the abortion of certain of the flowers. 
Internodal shortening is to be observed in some of the Silenez (subfamily 
of the Caryophyllaces), resulting in compound cymose inflorescences, 
resembling corymbs or umbels. Dianthus barbatus (the Sweet William) is 
a good example. 
The suppression of the original terminal flower of these continuous dichasia 
is nof uncommon. The first forking of the inflorescence then appears to be 
dichotomous, but is in reality only falsely so. 
Monochasia and Sympodial Cymes.—So far nothing has been said regarding 
the monochasium ; that is to say, of a cluster consisting of the terminal 
flower and a single lateral, arising from the axil of a leaf-structure below. 
From a comparative study of flower-clustering among Dicotyledons, there 
seems no evidence for assuming that the monochasium precedes the dichasium 
in the evolution of inflorescences. When a solitary terminal flower gives 
place, as it were, to a cluster, then not one but two (oceasionally three) 
lateral floral shoots are pushed out. ‘Ewin flowered clusters do occur in 
Dicotyledons, e. g., in the genus Geranium, but there is little doubt that 
these have come from umbel-like compound cymes through reduction. 
