277 
in the Root and Stem of Dicotyledons . 
rays of the hypocotyl. The interxylary phloem-system of 
Thladiantha is beyond comparison more highly developed a 
fact correlated no doubt with the presence of the root-tubers. 
The interxylary phloem in our plant differs from that in 
Bryonia 1 , (i) in the fact that it is in part formed directly 
from the cambium, (2) in having no constant relation to the 
tracheae. 
4. Ckiroizia pedu 7 icularis>lAnd\. (Gentianeae). In this genus 
the existence not only of the medullary phloem, which is 
usual in the order, but also of phloem-strands imbedded in 
the wood, was discovered by Vesque 2 in 1875. The species 
observed by him was C. linoides. His observations were 
extended by Solereder to C. baccifera and to Orphium frutes - 
cens*. We have been able fully to confirm the statements 
of these authors in the species examined by us. The 
medullary phloem forms a ring of scattered strands separated 
by a few cells (1-3) from the inner margin of the wood. 
Opposite the larger bundles the phloem-strands may form a 
double row. The external phloem is not much developed. 
In a stem, where the secondary wood was quite thirty ele- 
ments in radial thickness, the normal phloem had received 
scarcely any increase from the cambium. The groups of 
sieve-tubes are both smaller and less numerous than those in 
the pith, and the individual sieve-tubes are also smaller. In 
the external phloem ’015 mm. is a maximum diameter for the 
sieve-tubes, while in the internal strands *032 mm. is commonly 
attained. 
The examination of sections from near the apex proves 
that the medullary phloem is formed somewhat later than the 
external. The first medullary strands to be formed are those 
just within the large bundles, and here they reach their great- 
est development. Later on, phloem-strands are also differ- 
entiated on the inner side of the smaller bundles and the 
interfascicular tissue. As a rule it is not until two or three 
xylem-elements have been fully formed in each bundle, that 
1 Weiss, loc. cit., Flora, 1880, p. 109. 
2 Loc. cit., p. 146, PI. 10, Figs. 3 and 4. 3 Loc. cit., p. 182. 
