in the Root and Stem of Dicotyledons. 295 
so the contents of the phloem are chiefly conveyed to the 
cambium in order to be employed in the activity of this 
meristematic zone and in the building up of the xylem 1 .’ As 
evidence for this view, Dr. Blass, who has worked out the 
theory in detail, brings forward the facts that in trees the sieve- 
tubes nearest the cambium are richest in proteid contents ; 
that in some cases the contents of the phloem accumulate in 
autumn and are diminished when growth is renewed in the 
spring ; that in some plants with reduced xylem ( Drosera and 
certain aquatics) the sieve-tubes are rudimentary, containing 
nuclei and even chlorophyll-granules ; and lastly that in the 
ringing experiments so often quoted in support of the prevail- 
ing views, the excessive growth above the incision is due 
simply to the formation of ‘ wound- parenchyma,’ and not to 
the interruption of the downward current of food-material. 
In support of this contention, Dr. Blass states that the phloem 
below the wound shows no diminution of its contents. 
We purposely avoid criticising Dr. Blass’s arguments, 
though it appears to us that his results are not inconsistent 
with the theory of conduction and in some points even lend it 
additional support. We willingly admit that in all plants 
with cambial growth the supply of food-materials for such 
growth must be an important function of the phloem. Nor 
are we aware that this has ever been denied. But we wish to 
point out that the anatomical relations of the phloem are 
often quite inconsistent with the supposition that its exclu- 
sive or principal function is connected with the formation of 
wood. 
In all the numerous plants which have bicollateral bundles 
or an analogous arrangement of tissues, a great part of the 
phloem, often the greater part and sometimes nearly the 
whole, is placed in that region of the stem where no formation 
of wood is going on, in a position as remote as possible from 
the wood-producing cambium, for the rare exceptions in 
which some internal wood is also formed may here be left 
out of consideration. Yet this internal phloem is absolutely 
1 Loc. cit., p. 258. 
Y 
