256 BOTANICAL GAZETTE [Marcu 
those depicted in the latter illustration. The parenchyma in both 
is flanking only and the leaf trace plays a predominant part. 
Hence, from a consideration of the situation obtaining from the 
lower dicotyledons to the Compositae, it would seem clear that the 
herbaceous type has been derived from the woody through the con- 
version of segments related to the outgoing leaf strand into wood 
parenchyma; and that in extreme herbaceous types the storage 
tissue has become confined to the sides of the trace by the simple 
process of the thinning of the cylinder and the increased relative 
importance of the foliar strand. 
An interesting feature of some species of Solidago is the multi- 
plication of leaf traces, a situation which might be expected in rela- 
tion to the increased efficiency of the leaves. As has been stated, 
the usual number of traces in this genus is 3; but in more vigorous 
stems the leaf traces may be more numerous. In S. patula, for 
instance, there are 5; and in S. sempervirens, the salt marsh golden- 
rod, there are as many as 7 or 9, according to the vigor of the plant. 
This condition is represented in fig. 7, which is a transverse section 
of S. sempervirens. In the instances where there is a multiplication 
of leaf traces, it is noteworthy that in addition to stout and leafy 
stems, these species are likewise characterized by unusually large 
and full heads of flowers. 
Another point of interest, which is of course a common anatomi- 
cal characteristic of the Tubuliflorae, is the presence of oil canals 
in the pith or cortex, or in both. In fig. 7, which is a cross-section 
of S. sempervirens, these oil canals may easily be noted in both pith 
and cortex; and in fig. 5, which represents the same plane in 
S. canadensis, they are visible in the cortex only. 
An additional feature of interest is presented by the leaf bundles 
in the cortex, namely, the presence of internal phloem. This is 
shown in fig. 8, which is a high magnification of one of the cortical 
bundles of S. sempervirens. Other species of Solidago, for example, 
S. canadensis, S. patula, S. rigida, etc., show the same organization 
of their cortical bundles, and it seems to be a general condition for 
the genus. It has been suggested by WorspELL’ in the case of the 
Cucurbitaceae that internal phloem is a “vestigial structure.” In 
® WorspDELL, W. C., The origin of medullary (interxylary) phloem in the stems 
of dicotyledons. Ann. Botany 29:567-590. figs. 10. 1915 
