Dispersal of Herbaceous A ngio sperms. 549 
and reduction, has been generally current among geologists for some time, 
but the first definite statement of such a view which the writers have 
found is that made by Hallier (8) in 1905. In discussing the origin of 
the Angiosperms he states that ‘ from their arborescent habit (&c.) the 
Magnoliaceae are, without doubt, the oldest of living Angiosperm families, 
and down from them, through the Schizandreae, Lardizabaleae, Berberi- 
daceae, Ranunculaceae, and Nymphaeaceae, clear through to the Mono- 
cotyledons, there has been a continuous and unbroken line of reduction 
from the ancient arborescent forms to lianas, shrubs, undershrubs, herbs, 
and water-plants. ... In the Berberidaceae, Menispermaceae, and species of 
Clematis , the vascular bundles of the axis are already separated by the 
widening of the medullary rays ; and in the herbaceous Ranunculaceae (as 
well as in the Piperaceae and Chloranthaceae) by a much greater widening 
of the medullary rays, by an early cessation of cambial activity, and by the 
appearance of additional circles of vascular bundles, the type of stem which 
is characteristic of the Monocotyledons has been developed.’ 
Such an hypothesis of reduction from primitive arborescent forms has 
also been worked out under the direction of Professor Jeffrey by several 
members of his laboratory (12, 1, 1 and 5). Eames (5) in a paper devoted 
to the subject brings forward evidence that the earliest Dicotyledons 
possessed a solid tubular woody cylinder of considerable thickness which 
has gradually been reduced, and finally broken up into a circle of separate 
strands, the ‘ typical ’ herbaceous condition. 
A discussion of this general problem is the purpose of the present 
paper, in which the writers will bring forward evidence from the fields of 
palaeobotany, anatomy, phylogeny, and phytogeography in an attempt to 
come to some definite conclusion as to the relative antiquity of these two 
great types of plants, and as to how they have become dispersed over the 
world. 
I. Evidence from Palaeobotany. 
One naturally turns at first to geology in an endeavour to settle any 
phylogenetic problem, but in the question under consideration, as in so 
many others, evidence from this source, though of value, is not at all 
conclusive. 
The change of growth-habit during evolutionary history by some of the 
lower orders of vascular plants, as shown in a comparison between their 
ancient fossil forms and their living members, is perhaps of importance as 
indicating by analogy what may well have been the course of events among 
the Angiosperms. The ancient members of the lycopodiaceous and equisetal 
series, for example, were with few exceptions provided with well-marked 
secondary wood and in the great majority of cases were decidedly arborescent 
in habit. Their living representatives, however, the modern Lycopodiaceae, 
P p 2 
