586 Worsdell .— The Origin and Meaning of Medullary 
phloem. The internal phloem of the exterior bundles is well developed and 
separated from the protoxylem of the bundle by two or three ground-tissue 
elements; this fact, and the further one that most of the internal-phloem 
strands have xylem elements attached to their periphery at various points, 
shows clearly that the internal phloem of these exterior bundles represents 
an independent bundle, having 110 morphological connexion with the bundle 
opposite which it occurs. These internal-phloem groups of the outer 
bundle-series doubtless represent the vestige of a former bundle-series 
occurring between the two at present alone existing. 
The structure of Acanthosicyos thus affords plenty of evidence in 
support of the writer’s theory, and nothing which in any way contradicts it. 
Fig. 8 . Transverse section of normal stem of typical Cucurbitaceae, showing two series of bundles 
(1 and 2), each bundle with its strand of internal phloem {if), sc = sclerotic ring. (Diagrammatic.) 
Summary and Conclusions. 
The following are the main results of this investigation: 
1. The more conservative parts of the axial configuration, viz. the 
peduncle , and the node of the vegetative stem, are those in which ancestral 
traits in the structure are most likely to have been retained. 
3 . What are considered to be ancestral features have been found 
in these regions; but also, in some cases, in the internodal region of the 
vegetative stem. 
3. Questions and data relating to the ontogeny, such as the develop¬ 
ment of the internal phloem (or bundle) from the same desmogen strand 
as the bundle of the ring; or the primary or secondary (cambial) mode 
of development of parts of the internal-phloem bundle, are of no value 
for throwing light on the origin of the internal phloem (or bundle). 
4. In the vegetative stem of certain members of the order, and, 
as a rule, in its lower part only, the internal phloem exists in the form 
