2 QO Scott and Brebner. — On the Anatomy 
these various cases is obvious in the light of the develop- 
mental facts. 
It is a nearly constant rule that the island is bounded on its 
outer side by woody parenchyma ; its inner boundary is 
usually, but less constantly, formed by woody fibres. The 
xylem-elements abutting laterally on the islands may be ray- 
cells, woody parenchyma, or fibres. We have never found 
vessels in contact with the islands. On the outer side and on 
the two flanks the contrast between the thick-walled xylem 
and the soft phloem is quite sharp. On the inner side, how- 
ever, a layer or two of thin-walled cells are generally found 
between the woody fibres and the actual cambium, and among 
these cells developing xylem-elements may sometimes be 
observed. This proves that the phloem-forming cambium 
has not wholly lost its capacity for centrifugal formation 
of wood. 
The sectional form of a phloem-island is circular, or more 
often somewhat elliptical, with the major axis directed tan- 
gentially to the surface of the stem. Its cambial-layer is thus 
curved, with its convexity towards the centre of the stem. 
This is due to the fact that during the formation of the island 
the retardation of the wood-forming activity of its cambium 
begins at the middle point of the layer. 
As regards the minute structure of the phloem-islands we 
have nothing to add to de Bary’s account, except that the 
elongated cambial cells on the inner side are very conspicuous 
in radial section (Fig. 8). The phloem is made up of paren- 
chyma, sieve-tubes, and companion cells. The first-formed 
sieve-tubes of the island have approximately transverse sieve- 
plates (Fig. 8), but those which are developed later on have 
inclined terminal walls, sometimes bearing three sieve-plates 
each. The direction of inclination of these walls is variable, 
as would be expected from the curved course of the cambial 
layer, and from the great crowding of the cells. Anastomosis 
of the phloem-strands in the internodes is certainly rare, if it 
ever occurs, but they unite with one another at the nodes. 
