1921] JEFFREY & TORREY—HERBACEOUS ANGIOSPERMS 27 
foliar ray to which it is related. Further, the foliar ray becomes 
much more homogeneously parenchymatous in more advanced and 
herbaceous species, and does not contain the admixture of vascular 
and fibrous elements which reveal the mode of origin of the foliar 
rays in more woody and primitive species. 
The foliar ray surrounding and subtending the leaf trace is 
characteristic of the less advanced dicotyledonous herbs and of the 
lower more woody region of those higher in the herbaceous sequence. 
This type of ray gives place, by the later thinning of the woody 
cylinder, to one in which the storage tissue is confined to the flanks 
of the traces. The long vertical extension of these flanking rays 
results in the division of the originally continuous woody cylinder 
of the ancestral Dicotyledons into a circle of separate strands, the 
fibrovascular bundles. Of the strands thus resulting, those more 
closely related to leaves manifest an interesting contrast to the 
others because they very frequently manifest an absence of cambial 
activity. This cambial inactivity seems to be a safeguard against 
the undue consumption of assimilates in the growth in thickness of 
the foliar strands. Such idtinn in thickness would clearly not be 
advant ust dent for their success in thestruggle 
for exditence on nthe: amount Pr food stored up either in their stems or 
their seeds. The correctness of this interpretation of the undoubted 
fact that foliar traces lose or tend to lose their cambial activity 
in the stem of herbaceous Dicotyledons is vouched for by conditions 
observed in roots, to be enlarged upon in another connection. 
Roots permanently and perennially provided with root hairs are 
usually without secondary activity in the woody cylinder, while 
roots of allied species without persistent root hairs have the 
secondary tissues well developed. In other words, the more effi- 
ciently absorptive roots are without secondary growth, while roots 
of allied woody and less efficient species are well provided in this 
respect. In advanced herbs, such as the members of Ranunculus, 
the traces of leaves and roots stand out conspicuously in the 
subterranean stem by the absence of the secondary growth charac- 
teristically present in the fibrovascular strands of the stem proper. 
It appears clear from these considerations that the herbaceous 
type is the extreme expression of efficiency, and that the correlated 
