Dispersal of Herbaceous A ngio sperms. 553 
also indicated by the character of the anomalous and extrafascicular 
cambia which appear in many forms. These are almost always con- 
tinuous for a considerable distance around the stem and are not limited 
to the production of small bundles. 
From all the evidence, therefore, it seems reasonable to conclude 
that the occurrence of distinct ‘fascicular’ and ‘interfascicular’ cambia in 
herbaceous plants is the result of reduction and specialization from a primi- 
tively uniform and continuous condition of the secondary meristem. Such 
a conclusion is of course distinctly in favour of the view that herbs have 
been derived from plants possessing well-developed secondary wood. 
Aside from facts concerned with the origin of the cambium, evidence 
of value may also be derived from a study of the tissues which it 
lays down. In the secondary wood of very many herbaceous plants 
uniseriate medullary rays are either absent or represented by rows of 
vertical parenchyma cells, and in many cases vertical parenchyma of all 
kinds has entirely disappeared save in the vicinity of the huge vessels, 
thus leaving the mass of the wood composed simply of fibres. In the 
secondary xylem of all woody plants, both ancient and modern, radial 
parenchyma is always well developed ; and in the higher Conifers and all 
woody Dicotyledons vertical parenchyma, too, not associated with the 
medullary rays, is a characteristic feature. That these tissues should be 
absent from the secondary wood of so many herbaceous plants, therefore, 
is much more logically explained, as Eames has pointed out, by the 
great development of the broad segments 'of interfascicular parenchyma, 
which are quite sufficient for the storage and transportation of all food 
within the woody ring, and render unnecessary a development of smaller 
groups of radial or vertical parenchyma. Such a conclusion indicates 
again that the herbaceous type of stem is reduced rather than primitive 
in its character. 
All evidence from the anatomy of the secondary wood, therefore, 
lends strong support to the theory that woody plants are more ancient 
than herbs. To make the argument still more convincing, however, it is 
necessary to demonstrate clearly the manner in which the herbaceous 
type of structure has been developed from that of a woody stem. 
Hallier suggests, as we have noted above, that the many-bundled 
herbaceous stem has been derived by the increase in width of certain 
medullary rays, which break up the continuous cylinder into separate 
strands, but he elaborates no extensive theory. 
The only hypothesis which seems to have been formulated in detail 
is that originating with Professor Jeffrey and worked out under his 
direction by several students. In brief, this hypothesis explains the 
segments of interfascicular parenchyma which occur between the bundles 
of the herbaceous stem as due not to gradual increase in width of 
