Dispersal of Herbaceous A ngiosperms . 551 
Since the chief difference between woody plants and herbs consists in 
the presence or absence of an active cambium, the most important anato- 
mical facts for bur purpose are those concerned with the development of 
this meristematic layer, and the character of the tissues which it produces. 
Practically all herbaceous forms, at least among Dicotyledons, show evidences 
of cambial activity. This may be confined to the isolated vascular bundles 
themselves, as in the Monocotyledons and many Dicotyledons, where its 
activity is shown by the radial arrangement of some or all of the xylem 
and phloem elements ; or it may extend during later development across 
the interfascicular parenchyma which separates the bundles and cause 
a slight radial arrangement in this tissue also ; or it may form an un- 
broken ring of vascular elements arising simultaneously about the pith. 
The origin of secondary growth in most woody Dicotyledons follows the last 
category, the cambium appearing simultaneously throughout its whole extent. 
In others, however, especially stems with well-marked primary bundles and 
wide rays, it belongs to the second type, for the cambium is early active in 
laying down secondary wood opposite the protoxylem groups, but only 
later do these isolated Gambia become united into a continuous ring by 
their extension across the gaps between the bundles. It is this irregularity 
in the ontogenetic development of the vascular ring of herbs and woody 
plants which has been emphasized by Sachs and his followers, who have 
applied the term ‘ fascicular , to that part of the cambium which occurs 
opposite the primary strands, and ‘ interfascicular 5 to that which later arises 
between them. 
It is easy to attribute a phylogenetic importance to these facts of 
ontogeny, and to infer that the earlier stages in the development of the 
twig repeat, in a general way, conditions which obtained in ancient forms. 
To imagine that the stem of the ancient Dicotyledons was herbaceous in 
texture and supplied with a ring of separate primary bundles ; that cambial 
activity began first in these bundles, increasing them slightly in size, and 
that finally it became continuous across the intervening spaces and laid 
down an unbroken ring of secondary wood, thus making possible the 
development of woody plants, is a perfectly natural conclusion. It should 
be noted, however, that such a theory of phylogeny was not made by 
Sachs and his followers, who concerned themselves simply with the develop- 
ment of the individual ; nor have the writers been able to find it put forward 
in any of the common text-books. Doubtless the idea that herbs are more 
primitive than trees has been in the minds of many people, but the theory 
has been definitely formulated very rarely indeed. 
But do the anatomical facts, when carefully considered, give sound 
warrant for such a conclusion? The irregular development of the cambium 
may be regarded .with equal logic as a step towards its disruption and 
disappearance rather than as a primitive feature. On such a theory, herbs 
