The Origin and Meaning of Medullary (Intraxylary) 
Phloem in the Stems of Dicotyledons. 
I. Cucurbitaceae. 
BY 
W. C. WORSDELL. 
With ten Figures in the Text. 
Introduction. 
T HE object of botanical investigation, in whatever department, should 
be to determine, as far as possible, the interrelationship of the various 
facts which are accumulated, and arrange them accordingly ; and not 
merely, as has for so long been the custom, to pile them in a chaotic heap. 
This is well exemplified in the case of the study of ‘ internal phloem ’ 
in dicotyledonous stems. By this time we have a large, chaotic heap 
of facts with regard to this remarkable structure, facts which sadly need 
co-ordination. 
It has been discovered that this intraxylary phloem occurs in a large 
number of natural orders. In these different orders or groups it is seen to 
assume different forms. Very frequently it occurs as a continuous zone 
immediately within the xylem of the central cylinder on the extreme 
periphery of the pith ; or this zone may be broken up into separate groups 
of phloem. Sometimes such a phloem-group is more or less closely 
attached to the inner side of each bundle of the central cylinder. At 
other times the medullary bast takes the form of numerous separate 
strands scattered throughout the pith. Again, all or some of these features 
may be combined in one and the same plant or natural order. 
The writer’s object in the present series of papers is to endeavour 
to demonstrate, in those cases where this is at all possible, the meaning 
and origin of the intraxylary phloem. It is high time that an attempt 
was made in this direction, if the brake on the wheels of the chariot of 
progress is not to hamper for ever our efforts to obtain a glimpse of the 
unity of Nature in this particular field of anatomical structure. 
The writer considers that medullary phloem represents, probably in 
all cases, a vestigial structure , the remnant of a former system of medullary 
vascular bundles in which the xylem has disappeared. This has, indeed, 
[Annals of Botany, Vol. XXIX, No. CXVI. October, 1915.] 
Pp 
