Hill . — On the Seedling- Structure of certain Piper ales, 165 
could be made out ; if it takes place, it must do so during its inward 
passage from the node, but what probably occurs is that the metaxylem 
elements overtake and pass the protoxylem, so that the latter become 
exarch. A diarch root-structure is thus formed directly the two strands 
meet in the centre of the axis. 
Other seedlings showed what is probably the normal course, viz. each 
endarch bundle of the cotyledon petiole, as it passes downwards towards 
the node, exhibits a bifurcation of the phloem and a rotation of the xylem 
as described for Piper , but this rearrangement in Peperomia eburnea is not 
nearly so decided as in Piper. 
A further anomaly was exhibited by another seedling of this same 
species ; the cotyledonary bundles showed the normal rearrangement, but 
one also possessed a group of phloem elements on the protoxylem side 
of the strand. This extra phloem decreased in amount, so that by the time 
the centre of the axis was reached it consisted of but a few elements which 
still retained their abnormal position internal to the protoxylem. Ultimately 
they entirely disappeared. 
This same specimen was also peculiar, inasmuch as a normal root- 
structure took much longer to form than in other individuals of the same 
species. 
Peperomia pellucida , H. B. K. One vascular bundle enters the distal 
end of each petiole from the cotyledon (Fig. 13). Tracing the strand 
downwards, the phloem gradually forms two groups of elements as in 
Pep. eburnea , but frequently this bifurcation is not equally well marked 
in the bundle of each seed-leaf petiole. Immediately before the node 
is reached there is a suggestion of the protoxylem taking up an exarch 
position. 
The cotyledonary traces pass inwards as relatively broad bands ; the 
phloem groups of each strand separate and pass to opposite sides of 
the central cylinder, where they come into contact with the plumular 
bundles which, in the youngest seedling examined, were still in a pro- 
cambial state and arranged in two groups, one on each side of the central 
cylinder, and separated by parenchymatous elements. Thus the two 
phloems of the root result. 
Concurrently, the xylem follows a centripetal course, the metaxylem 
travels further inwards, thus leaving the protoxylem in an exarch position ; 
these elements are very few in number, there being one on one side and 
two on the other. The tracheae are irregularly disposed, and there is 
no diarch plate such as obtains in Piper , at about this stage (Fig. 14). 
Following these structures downwards, new xylem elements may make 
their appearance external to, and in contact with, the existing protoxylem. 
Further, it is seen that these elements follow an undulating course, so that 
in one transverse section they may be in contact with the metaxylem 
