Dispersal of Herbaceous Angiosperms. 559 
a broad-rayed woody form is shown in Diagrams 3 and 4 ; and in PI. XXXIX, 
Fig. 12, and PL XL, Figs. 13, 14 and 15, and 16 and 17. 
In certain cases there has indeed been a conversion of portions of 
the woody ring into parenchymatous or fibrous tissue, as is shown in 
Fig. 7, a transverse section of an herbaceous stem of Salvia ; and in 
Diagram 2. In all such instances, however,- the conversion is not opposite 
the protoxylem , as Jeffrey’s theory supposes, but opposite the gap between 
the protoxylem clusters. Instead of a single ray becoming very high and 
wide and constituting the interfascicular parenchyma, as in most multi- 
fasciculate herbs, a whole segment, including a number of small rays and 
their adjacent vertical fibres and vessels, becomes thin-walled and more or 
less parenchymatous. The vertical elements never tend to become hori- 
zontal, however, and the structure is not comparable to the ‘ aggregation ' 
and ‘ compounding’ of rays observable in certain woody families. In some 
cases the interfascicular parenchyma seems to owe its origin both to increase 
in width of rays and to conversion of woody elements into parenchyma 
. (PI. XXXIX, Figs. 10 and 11). 
Most vines have the structure of multifasciculate herbs (PL XL, Fig. 18). 
The rays opposite the gaps become very wide, and those in the fascicular 
segments usually disappear. 
It seems clear, therefore, that in the development of all herbaceous 
stems a simple reduction in the amount of secondary wood has been the 
chief factor ; and that this has been supplemented by the increase in bulk, 
to a greater or less degree, of the ordinary parenchymatous tissue. Instead 
of calling upon a subterranean rhizome to furnish an intermediate condition 
between related woody and herbaceous stems we can find these transitions 
clearly shown in different parts of the woody axis. The base of most 
herbaceous stems is much stouter than the upper portion, and often shows 
a close resemblance to a woody twig. On passing upward from such 
a base to the more delicate portions of the stem, we can readily observe the 
progressive decrease in cambial activity and increase in parenchymatous tissue 
which have caused the development of the herbaceous type. PL XXXIX, 
Fig. 1, a cross-section of a somewhat decumbent aerial stem of Arctotis 
grandis , shows in one plane the transition from a continuous woody stem 
to one where the bundles are quite isolated in a true herbaceous fashion. 
The main point to be emphasized in this anatomical study of the 
evolution of herbs is that an herbaceous stem, in all its essentials, is like the 
first annual ring of its woody relatives. If this has a continuous ring of 
primary and secondary wood, as do the twigs of woody species of Nicotiana , 
Hypericum , and Hibiscus (PL XXXIX, Figs. 5, 3, and 8), the corresponding 
herbaceous stem will show the same features (PL XXXIX, Figs. 6, 4, and 9). 
If the woody form possesses wider rays and an interrupted primary cylinder, 
as does Xanthorrhiza and the arborescent species of Acanthopanax and 
