178 Scott. — On some points in the Anatomy of 
phloem). With these strands the medullary phloem remains 
in permanent continuity. Thus the interxylary phloem of 
the transitional region is in communication both with the 
medullary and the external phloem-systems of stem and 
root. 
A further complication of structure appears in the older 
hypocotyl, for an internal cambium arises by the divisions of 
the outer cells of the pith, starting from the internal phloem- 
groups, and sometimes extending nearly round the whole 
circumference. It produces some additional medullary phloem 
internally, and also gives rise occasionally to a few lignified 
elements on the side towards the wood. 
The chief points then to be noted are the following : — 
1. The internal phloem extends downwards into the hy- 
pocotyl and passes out between the converging protoxylem 
groups of each cotyledonary pair of bundles, thus joining the 
external phloem of the root. 
2. The hypocotyl and the adjacent parts of stem and 
root have a complex secondary wood containing numerous 
strands of interxylary phloem, imbedded in parenchyma. 
These c phloem-islands ’ are produced centrifugally by the 
cambium. 
As regards the course of the internal phloem in the transi- 
tion from stem to root, Ipomoea versicolor may be taken as 
typical of plants with bicollateral bundles generally. A full 
discussion of this subject, with references to the literature, 
will be found in a forthcoming paper by Mr. Brebner and 
myself. 
I am not aware that the existence of phloem-islands in the 
wood has previously been observed in any Convolvulaceae. 
The very remarkable anomalies described by Schmitz 1 and 
Dutailly 2 in the roots of certain perennial members of the 
1 tiber die Anat. Structur der perennirenden Convolvulaceen-Wurzeln, Bot. 
Zeitung, 1875, p. 677. His results are summarized by de Bary, Comp. Anat., 
Eng. ed. p. 606. Tschirch, Angewandte Pflanzenanatomie, 1889, figures a trans- 
verse section of the root of Ipomoea Purga. 
2 Sur quelques phenomenes . . . dans le tige et la racine des D icotyledones, 
Paris, 1879. 
