in the Root and Stem of Dicotyledons . 281 
doubt that the cambium lies to the outside of the sieve-tubes 
all through. 
Chironia and Strychnos are the only genera in which we 
have at present found strictly medullary phloem in the root, 
phloem, that is, which lies altogether within the primary 
xylem. In both cases its presence is somewhat inconstant. 
On the whole the agreement in structure between root and 
stem is exceptionally manifest in Chironia . The material at 
our disposal did not permit of our tracing the actual transition 
from the one to the other, for all the roots available were 
adventitious. As regards the connection of these roots with 
the stem, we found that the interxylary and medullary phloem- 
strands of the adventitious root are continuous with the inter- 
xylary phloem of the stem, but there is no direct communi- 
cation with the medullary phloem of the latter. 
In Gentiana acaulis , L., which we also examined, the root, 
though very parenchymatous, showed no internal or inter- 
xylary phloem. In other Gentianeae, however, peculiarities 
resembling those of Chironia and Orphium have been 
observed. Thus Arthur Meyer in his admirable monograph 
of Gentiana lutea 1 describes sieve-tubes in the secondary 
wood of both stem and root of that species 2 . He states that 
G. punctata, pannonica y and purpurea agree anatomically with 
G. lutea. 
In G. cruciata , Jost 3 found phloem-strands in the secondary 
wood of the stem, but not of the root. Weiss also found 
interxylary phloem in the fleshy roots of some Gentianeae 4 . 
It is evident that the anatomy of the order will repay further 
investigation, especially as regards the relation between stem- 
and root-structure. 
We examined a considerable number of other roots of 
plants with bicollateral bundles, but the results do not call for 
1 A. Meyer, Beitrage zur Kenntniss pharmaceutisch wichtiger Gewachse, V. 
Ueber Gentiana lutea , &c. Archiv fur Pharmacie, 3te Reihe, Bd. XXI. 1883. 
2 Loc. cit., pp. 502, 569. 
3 L. Jost, Die Zerkluftungen einiger Rhizome und Wurzeln ; Bot. Zeitung, 1890, 
p. 442. 
4 Loc. cit., Bot. Centralblatt, XV. p. 410. No details are given. 
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