The Origin and Meaning of Medullary (Intraxylary) 
Phloem in the Stems of Dicotyledons. 
II. Compositae. 
BY 
W. C. WORSDELL. 
With twenty-seven Figures in the Text. 
Introductory. 
I N the issue of this journal for October, 1916, the writer set forth the 
essential features of the vascular structure of the axial and foliar organs 
of the Cucurbitaceae, showing that this structure is fundamentally a ‘ Mono- 
cotyledonous ’ one, consisting of a system of scattered bundles of which the 
‘ internal-phloem 5 strands constitute an inner series, having completely lost 
their xylem. 
It can be deduced from the facts presented in this paper that the 
vascular structure of the stems and leaves of Compositae belongs to the same 
type, having also been derived from an ancestral scattered or ‘ Mono- 
cotyledonous ’ system of bundles. Eor the Compositae represent one of the 
Natural Orders many members of which exhibit ‘ internal ’ or medullary 
phloem in their stems, and it can be shown that the medullary phloem- 
strands really represent an innermost series of vascular bundles belonging to 
the primitive scattered system. 1 
What was stated in the previous paper, viz. that such relatively conser- 
vative organs as the mature stem, peduncle, and foliage-leaf are to be studied 
in connexion with ancestral characters of this kind rather than the seedling 
stem, is here again emphasized. 
It will thus be seen that the view-point from which the subject is 
envisaged is entirely different from that of any of the authors mentioned 
below or, indeed, from that of any previous investigator. Hence the treat- 
ment of the subject is different, viz. along lines which tend to emphasize 
chiefly those facts which have more directly and obviously to do with the 
main thesis. Many details of fact which are inessential to the elucidation of 
1 In the following pages the structure is usually described as seen in transverse section. 
[Annals of Botany, Vol.XXXlII. No. CXXXII. October, 1919.] 
