590 Worsdell.—Medullary Phloem in Stems of Dicotyledons . 
27. The conclusion is reached that the vascular system of Cucurbitaceae 
represents the vestige of a former ancestral scattered system of bundles such 
as obtains in Monocotyledons, of which only two series or rings remain in 
perfect condition, the rest appearing in the form of rudimentary external 
phloem-strands (rarely bundles as well), ‘ internal-phloem ’ strands, and 
medullary bundles or phloem-strands (Figs. 8, 9, 10). 
28. The sinuous contour of the bundle-ring in most Cucurbitaceae 
is the expression of the partial congestion of two bundle-series into one— 
an intermediate condition between the cylindric and the scattered system. 
29. Such a structure as the internal-phloem strand must be investi¬ 
gated both from the morphological and physiological standpoints. Its 
function, ontogeny, and phylogeny must all equally receive consideration. 
The writer is indebted to the authorities of the Royal Gardens, Kew, 
for much of the material used in this study. 
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