Arher. — On the Roots of Medullosa anglica . 431 
This is no doubt the primary phloem (b 1 .). It corresponds 
very closely to the primary phloem in the stem of Heter- 
angium tiliaeoides 1 . In this section the primary phloem is 
very clearly marked off from the outer large-celled tissue, 
the pericyle. 
The Secondary Roots. 
The main points in the structure and origin of the secondary 
roots of Medullosa have been already described by Dr. Scott 2 . 
The examination of a large series of sections of a root con- 
tained in the Binney material has, however, resulted in the 
elucidation of a few additional details. 
The transverse section of a root figured on PI. XX, Fig. 6, 
shows the base of a rootlet or secondary root (r./.). The 
structure of the root itself is precisely similar to that just 
described (Fig. 1 ). The particular rootlet shown in the 
photograph is, however, stunted and abnormal. The xylem- 
elements are very small, and much less developed than is 
usually the case, and probably the rootlet never functioned as 
a typical root. 
The lateral roots arise in three rows on the roots, at points 
opposite the protoxylem-groups. There is apparently, in all 
the roots which I have examined, some little distance between 
successive lateral roots in the same row ; and only one rootlet 
is given off in any one transverse plane. The ramification is 
therefore not so abundant as in certain roots of Lygino - 
dendron 3 . 
The xylem-strand of the rootlet arises, as we have seen, 
opposite a protoxylem-group of the triarch root. It then 
passes outwards obliquely, and not at right angles to the stele 
of the root, as in Lyginodendron 4 . The parenchymatous 
tissues of the rootlet arise from the divisions of a group of 
meristematic cells, probably of pericyclic origin, which cause 
a protrusion of the periderm of the root at some little distance 
1 Williamson and Scott, loc. cit., p. 761, PI. XXIX, Fig. 35. 
3 Scott, loc. cit., p. 103, PI. VIII, photos 19 and 21. 
3 Williamson and Scott, loc. cit., p. 740. 
* Ibid. 
