Dispersal of Herbaceous Angiosperms. 555 
development of an herbaceous stem, according to such a theory, are 
presented successively in Diagrams 1, 7, and 8. 
Although this hypothesis accounts for many of the facts in the 
Rosaceae, it meets with difficulty when applied to other families and is 
open to criticism on several counts. 
In the first place, the supposed transitional stages from a woody to 
an herbaceous condition which it cites, and which form indeed the 
strongest evidence in its support, are found not in the aerial parts of the 
stem but in its underground portions. In this region, however, the 
absence of mechanical strain and the necessity for storage operate to 
modify the vascular structures profoundly. Roots and rhizomes of 
almost all plants, because of their storage function, show areas in which 
the number of parenchyma cells has become so very large that whole 
segments of the woody cylinder have in fact been converted into paren- 
chyma. One would hardly expect intermediate steps between woody 
plants and herbs to originate in such a specialized underground region or 
to persist there, but such transitional conditions would naturally be 
sought rather in the aerial stems themselves, where the actual evolu- 
tionary development must have taken place. The fact that intermediate 
stages in harmony with the theory which we are criticizing are so rare in 
aerial stems must be regarded as one of its weak points. 
That the localization of primary wood has been one of the chief 
factors in the origin of the herbaceous stem also appears rather doubtful 
when we observe that so many typically woody plants, such as most 
Araliaceae, Fagaceae, Betulaceae, Proteaceae, and others, which belong to 
families containing practically no herbs, possess a ring of primary wood 
which is composed of very distinct bundles ; and that an enormous number 
of herbs have a perfectly continuous vascular ring. 
The fact, however, which militates most strongly against the validity 
of the hypothesis under discussion is that, in practically all many-bundled 
herbaceous stems, the interfascicular parenchyma is not subtended by tiny 
leaf-trace bundles, nor is the stem composed of the presumably typical 
‘ alternating large and small bundles, the latter being leaf-traces On the 
contrary, all the bundles in the aerial stem of a multifasciculate herb tend to 
be of the same general size, the leaf-traces in the stem usually growing 
a little smaller as they near their point of departure. At this point, also, 
the segment of secondary wood which each of them subtends usually 
grows smaller, too, and may become partially disintegrated into paren- 
chyma. It cannot well be called a compound ray, however, and it most 
certainly does not correspond to the interfascicular parenchyma, for this 
latter tissue is not subtended by protoxylem, but seems rather to repre- 
sent in most cases an ordinary medullary ray which has grown very wide. 
This failure of the theory of Jeffrey and his school to explain the stem 
