Hill. — On the Seedling-Structure of certain Piper ales, i 7 1 
amplexifolia , Pep. tithymaloides , and Pep. maculosa . in which . no such 
rearrangement takes place. These two groups merge imperceptibly one 
into the other; and further, a gradual reduction in the transition phenomena 
may be traced from Piper cornifolium , which forms one extreme, to 
Peperomia tithymaloides , which forms the other extreme. In the first case 
the vascular tissue of the root is derived chiefly from the cotyledons, while 
in the last the seed-leaf traces are unimportant ; the plumular bundles 
playing the prominent part. 
The absence of rotation in the xylem of the seed-leaf bundles is 
seemingly not confined to Peperomia. Chauveaud 1 has described what 
appears to be a similar case in the Labiatae. He remarks : ‘ Dans le Lamium 
album . . . les deux faisceaux ligneux primaires de la radicule se continuent 
j usque dans les cotyledons, en demeurant toujours dans le raeme plan, qui 
est le plan de symetrie des cotyledons. Ces faisceaux ne se partagent pas 
en deux masses et aucune rotation n’intervient.’ 
Saururaceae. 
Houttuynia cordata , Thunb. The transition phenomena are similar to 
those already described for Peperomia. The petioles of the seed-leaves 
form a short tube round the axis ; each contains one bundle, which, through- 
out its course, remains collateral with its protoxylem endarch in position. 
These bundles have their xylem but feebly developed, there being not more 
than two or three elements in each strand. On arriving near the centre of 
the axis the phloem branches to the right and left of the xylem, the corre- 
sponding groups fusing to form the two phloem masses of the roots. 
Concurrently, during the inward passage there is seemingly a rearrange- 
ment of the xylem, which results in the smallest elements being exarch in 
position. Metaxylem appears ; a root-structure with a typical diarch plate 
results (Figs. 16 and 17). 
In older seedlings the cotyledonary tube is better marked, and their 
bundles have more xylem (Fig. 15). 
The plumular traces fuse together, forming two fairly large collateral 
bundles occupying the centre of the axis, one on each side. As in Pep. 
polystachya and Pep. amplexifolia , the bifurcation of the cotyledonary 
phloem is very unequal, sometimes almost non-existent, inasmuch as 
practically the whole of this tissue from one seed-leaf bundle may fuse with 
the bast of one of the two plumular strands. This inequality of distribution 
is most marked in the older seedlings, and the reason for its occurrence 
may be to render each phloem group of the root equal in size. 
The xylem of the cotyledon-bundles of the older seedlings behaves in 
the manner already described : there is, however, a certain amount of 
1 Chauveaud, M. G. Sur la persistance de la structure alterne dans les cotyledons du Lamier 
blanc et de plusieurs autres Labiees. Comptes Rendus, 21 mars 1904. 
