and Histogeny of Stryckuos. 281 
is arranged in regular radial rows (only two elements in 
each row usually having thickened walls). This points to 
the occurrence of regular cambial divisions even at this 
early stage. The interfascicular tissue also shows a radial, 
though less regular arrangement of its cells. The small 
external phloem-groups, evidently produced by cell-divisions 
in all directions equally, are in immediate contact with 
the pericycle. There are usually two of these groups to 
each bundle, but they also occur opposite the interfascicular 
tissue. The internal (medullary) phloem groups are much 
larger than the external ones, though only about half as 
numerous. It may be estimated that they already contain 
collectively twice as many cells as there are in the external 
phloem. The cells of the medullary phloem show some 
signs of a radial arrangement (cf. Fig. 1). The pith is 
thin-walled throughout. It is clear then that the medullary 
phloem is a primary formation developed simultaneously 
with the protoxylem and the external phloem, and that thus 
the bundles are bicollateral from the first. The internal 
phloem accompanies the bundles on their exit into the leaf. 
The transverse section of a petiole shows five bundles, ar- 
ranged in a curved row, concave towards the upper surface. 
All these bundles are bicollateral, the superior phloem-groups 
being often more developed than the inferior. In the main 
bundles of the lamina, the bicollateral structure is still pre- 
served, both phloem-groups having about the same extent ; 
the smaller bundles, however, are of the normal collateral 
type with inferior phloem only. The medullary phloem of 
Strychnos thus possesses the characters which Petersen 1 and 
Weiss 2 have found to be general in other bicollateral bundles. 
It forms an integral part of the leaf-trace bundle to which 
it belongs. 
De Bary did not decide whether the normal external 
1 Ueber das Auftreten bicollateraler Gefassbiindel, u. s. w., in Engler’s Jahrbuch 
fur Systematik, Bd. iii, 1882, p. 391. 
2 Markstandiges Gefassbiindelsystem und Blattspuren, in Bot. Centralblatt, Bd. 
xv, 1883, pp. 396, 401. 
