294 Scott and Brebner . — On Internal Phloem 
just inside or just outside the protoxylem. It produces a 
large amount of medullary wood and phloem, with inverted 
orientation. 
2. The concentric bands of phloem and xylem, of which 
the secondary tissues are composed, are due to the activity of 
successive cambial layers, as was conjectured by Kruger and 
Solereder. 
Conclusion. 
In concluding we wish to point out the bearing of our 
subject on a theory which has been recently put forward as to 
the function of the phloem in general. 
In opposition to the prevailing view that the phloem is 
primarily the conducting tissue for the nitrogenous, and 
especially for the proteid, food-substances of the plant, Prof. 
Frank 1 and Dr. Blass 2 maintain that the phloem is essentially 
a store-tissue for the benefit of the wood. Prof. Frank says 3 : 
‘ The position which this tissue invariably ^occupies speaks 
most clearly for its function as a store-chamber of those 
substances which the cambial layer requires for the formation 
of the wood ; for in all fibrovascular strands it is a faithful 
companion of the woody bundles, and it increases and dimin- 
ishes in amount with the bulk of the woody bundle which is 
to be formed ; it is constantly situated immediately outside 
the cambial layer ; it forms an annular zone around the cam- 
bial ring where the latter surrounds a closed cylinder of 
wood, as in most dicotyledonous stems and trunks ; it forms 
an isolated strand, placed exactly in front of the woody 
bundle with its cambium, when we have to do with isolated 
fibrovascular-strands, as is especially the case in the petioles 
and ribs of the leaf.’ Dr. Blass, who worked in conjunction 
with Prof. Frank, expresses his views as follows : ‘Just as the 
contents of the starch-sheath serve to build up the bast-cells, 
1 Lehrbuch der Pflanzenphysiologie, 1890. 
2 Untersuchungen iiber die physiologische Bedeutung des Siebtheils der Gefass- 
biindel ; Pringsheim’s Jahrbiicher, Bd. XXII, 1890. 
3 Loc. cit., p. 162. 
