580 Worsdell .— The Origin and Meaning of Medullary 
appeared to be double. These facts also strongly support the view that the 
internal phloem represents an independent bundle. 
Two or three of the internal-phloem strands possess woody elements 
(vessels and fibres) on their outer side, a fact which of course rounds off the 
evidence, already partly supplied by the above-mentioned facts, that the 
internal phloem in this genus represents an independent bundle which has, 
for the most part, lost its xylem, 
Citrullus vulgaris. 
Seedling. 
In the transitional region between the hypocotyl and the root the 
internal-phloem strands, of which each bundle may have two or three, pass 
out along the side of the bundle and unite with the external phloem, leaving 
the bundles completely free from internal phloem before the protoxylem 
begins to rotate. 
This phenomenon, which was also noted in Lagenaria , appears to 
prove that the internal-phloem strand is not a constituent part of the bundle , 
as it moves quite independently of the latter, and at a different time, 
behaving, in fact, exactly like an independent medullary bundle. 
C. ecirrhosus. 
Stem. 
This plant was collected by the writer in the Namib desert of Damara- 
land in 1910. The stem is prostrate and trailing, with a structure like that 
of a root, for there is hardly any pith. 
There is a large amount of secondary 
wood, with wide-lumined vessels. 
The usual internal phloem is present. 
The rays are wide. 
The limit of the cylinder is indicated 
by isolated groups of fibres. 
Peduncle of Fruit. 
In the swollen part of this organ 
immediately below the attachment of the 
fruit is a ring of bundles’ possessing not 
nearly so much secondary wood as in the 
case of the stem-bundles, and enclosing 
a somewhat wider pith. The internal- 
phloem strands of the stem are here 
represented by vascular bundles which clearly belong to the amphivasal type, 
but, in some cases, are reduced therefrom, having xylem on their outer side 
Fig. 3. Citrullus ecirrhosus. 
verse section of the ring-bundles 
ternal-phloem strands of the stem. 
Trans- 
and in. 
x 11. 
