1918] WHITAKER—ANATOMY OF SOLIDAGO 257 
this family (the Cucurbitaceae), as is well known, the stem bundles 
are characterized by the presence of internal phloem. The con- 
clusion has been reached by this author, as a result of the study of 
the conservative regions, that the internal phloem is derived from 
inversely oriented medullary bundles fused with the inner surface 
of the woody cylinder. The situation in Solidago (and in other 
genera of the Compositae) is of interest in this connection, espe- 
cially as the presence of internal phloem is so constant a feature 
of the organization of the leaf trace in its course through the cortex. 
Since the results of comparative anatomical study of existing and 
extinct gymnosperms show clearly the conservative character of the 
leaf trace, it seems fairly obvious that the Compositae once 
possessed internal phloem in the stem like the Cucurbitaceae, 
Solanaceae, etc., but have lost it as a result of subsequent 
modifications. It may be pointed out that this assumption 
accords with the high systematic position ordinarily assigned to 
the family. This conclusion is in no way weakened by the fact 
that the Compositae are actually included in the same large 
group or cohort as the Cucurbitaceae, namely, the Campanulales 
(Campanulatae). 
In Solidago and most genera of the Compositae there are depres- 
sions in the woody cylinder corresponding to the leaf trace segments. 
Work carried on in this laboratory by Mr. J. P. Poote on Helianthus 
has demonstrated that in this genus the depressions invariably 
correspond to the foliar segment. Fig. 9, which is a woody stem 
of H. hirsutus, is inserted here because it illustrates this situation 
so diagrammatically. -At either side two median traces are to be 
seen, and also their two corresponding lateral traces, making in 
all 6 depressions in the cylinder and 6 corresponding parenchyma- 
tous modifications. Most species of Solidago show similar depres- 
sions in immediate relation to the foliar segment. Barrey’ has 
made it clear that in the oak these depressed segments are caused 
by the retarding influence on growth of pairs of closely approxi- 
mated compound foliar rays. The depressions in the Compositae 
in relation to the leaf trace segments are likewise connected with 
growth mechanics. 
‘ Battey, I. W., The evolutionary history of the foliar ray. Ann. Botany 26:647- 
661. pls. 62-6 Ef 
