1921] JEFFREY & TORREY—HERBACEOUS ANGIOSPERMS II 
Fig. 21 shows the very herbaceous stem of Aster tataricus, 
which differs from the American species in the strikingly soft 
texture and great vigor and thickness of its stem. This condition 
is shown in the transverse section by the large pith surrounded by a 
series of a distinctly separated and slender fibrovascular bundles. 
Another distinguishing feature is the large number of foliar traces 
which proceed from each leaf, these being as many as 7 (as may 
be seen in the upper region of the figure) in contrast with the 3 
which mark the numerous woody species of Aster. It is clear, 
therefore, that A. fataricus is a particularly well developed herb, 
and in this respect presents a marked contrast with the predomi- 
nantly woody herbaceous species of Aster. The roots of A. tataricus 
are like those of A. wmbellatus in that they are permanently 
without development of the secondary wood, and likewise have 
persistent root hairs, albeit these are much more delicate than 
in the latter species. 
Bringing together these results, we conclude that in woody 
species of Aster persistent root hairs and absence of secondary 
wood are correlated features of the organization of the root. In 
roots with evanescent root hairs the disappearance of these marks 
the beginning of the secondary activities in the wood. In Aster 
tataricus, which is remarkably herbaceous in its general habit in 
contrast with the species of the genus as a whole, a similar correla- 
tion is found between the persistence of root hairs and the absence 
of secondary growth. This will not be discussed further at the 
present time, but it will elsewhere be shown that there is a general 
correlation between a high absorptive capacity of the root 
(associated morphologically with persistent root hairs) and the 
absence of secondary woody developments in the central cylinder 
of the root. In other words, the herbaceous habit in roots is 
marked both by high absorptive efficiency and by the absence of 
secondary woody growth. 
In the light of these preliminary results in the case of the root, 
the situation already described for the leaf traces of Helianthus 
becomes particularly significant. A general examination of the 
species of this genus, particularly of those presenting in a more 
marked degree the herbaceous habit, indicates that cambial activity 
