Eric Drabble. 
64 
arranged in a ring, and the phloem loses all connection with the 
individual xylem-groups, and is found in a very irregular circle 
with numerous gaps, (Fig. 8, viii.), lying quite peripherally to the 
xylem groups. The xylem groups assume the form of a series of 
semilunar structures with the horns directed externally. About 
this stage the endarch protoxylem disappears, and a little lower 
protoxylem appears at the extremities of the horns, (Fig. 1, ix.), the 
change from the endarch to the exarch position being accom¬ 
plished very rapidly. At the same time the phloem has taken 
the form of a continuous ring. These changes deserve a little 
more detailed consideration. Apparently what really happens 
is that in the upper regions of the hypocotyl and in the plumule 
and cotyledon, the lignification of the xylem commences in an 
endarch position and proceeds centrifugally, while in the root and 
the lower part of the hypocotyl it commences in an exarch position 
and proceeds centripetally. The downward extension of the 
endarch protoxlem and the upward extension of the exarch, do not 
appear to meet, nor do they overlap; and there is a very short 
region in the hypocotyl where there are no spirally or annularly 
thickened elements at all. This is just at the very slowly 
extending, or almost non-extending, portion of the hypocotyl, and it 
is not altogether surprising to find an absence of the kind of 
element adapted to rapidly extended regions. A similar state of 
affairs was observed by Miss Edith Chick 1 in Torreya. 
Whilst these changes have been progressing the phloem ring 
has been broken up into twice as many strands as there are 
xylem groups ; a phloem group now lies in the arms of each xylem 
V, and one between each adjacent pair of V’s. These last named 
phloem groups are accompanied externally by an inwardly pro¬ 
jecting sclerenchymatous mass of pericylic fibres (Fig. 8, ix.) 
At first sight the impression that the phloem groups opposite the 
fibrous masses have been pushed centrally by the development of 
the latter is very strong, but there is no histological evidence of 
any crushing of the tissues in their neighbourhood. 
Lower down the xylem V’s become discontinuous centrally, 
and thus a phloem group alternates radially with each xylem 
group and the typical root-structure is attained. 
Oreodoxa regia. 
The mode of transition is essentially similar to that in 
Livistona mauritana , but the central cylinder has ground-tissue of 
so densly lignified a character that it is more difficult to trace the 
1 Chick, Miss E., New Phytologist, Vol. II., pp. 86—88. 
