296 Scott and Brebner . — On Internal Phloem 
typical in structure and contents. Nor is it a merely transi- 
tory tissue. Long after it is cut off from the normal cambium 
by a broad zone of secondary wood, it goes on increasing, 
often to a much greater extent than the normal external 
phloem. In many of these plants it is the latter, the phloem 
in contact with the wood-producing cambium, which is tend- 
ing to become rudimentary, while the internal phloem, 
remote from the cambium, is abundantly developed and 
retains all its typical characters. 
That the internal, like any other phloem, indirectly supplies 
the cambium as well as other growing regions, we do not for 
a moment doubt, but this is simply to say that it is a conduc- 
ting tissue. 
So too with the ‘phloem-islands.’ In plants like Strychnos 
or Salvadora these are no sooner formed than they become 
imbedded in the dense wood, and are cut off from all direct 
communication with the cambium. It would be easy to cite 
other examples, as the stem of the Chenopodiaceae and 
many allied orders, in which almost all the phloem is deeply 
imbedded in the fully formed wood, or the Monocotyledons 
generally, where the closed bundles retain a typical and active 
phloem for months or years after all formation of wood has 
been completed. 
In the light of facts such as these we cannot but think 
that the view of Prof. Frank and Dr. Blass depends on too 
one-sided a consideration of typical dicotyledonous anatomy. 
The passage quoted above from the former author, as well 
as Dr. Blass’s concluding statement that ‘ a typical condition 
of the sieve-tubes is only to be found where wood-elements 
are to be formed V seem to us not to be justified by facts. 
Our results as to the continuity of the various phloem-systems 
in root and stem tend to give further anatomical support to 
the theory of the conducting functions of this tissue, a theory 
which, as we need hardly point out, is fully consistent with the 
view of Prof. Sachs that the phloem may also be the seat of 
proteid-formation. 
1 Loc. cit, p. 290. 
