Seedling Structure of certain Centrospermae. 179 
strands fused on to the central ones, which in the petiole bifurcated and 
rotated in the usual way (Diagram 2, Figs. 1 and 2). In the case of the 
cotyledon c. 2 there are thus two pairs of phloem-masses and two groups of 
protoxylem-elements. Fusion takes place between the phloems which lie 
side by side, and the resulting strand remains in position, whilst the other 
two rotate inwards (Diagram 2, Fig. 3). The completion of these rearrange- 
ments in the axis results in a triarch root-structure (Diagram 2, Figs. 4 
and 5). 
Dianthus barbatus , L. The mode of transition is that of type 3. The 
lateral bundles in the base of the blade of the seed-leaves fuse on to the 
central bundles so that one strand only occurs in each cotyledon petiole. 
Although these bundles commence their division at the top of the cotyle- 
donary tube, the major part of the transition takes place during the inward 
passage of these strands to the centre of the axis, and in the upper part of 
the hypocotyl. 
Dianthus chinensis , L., differs from D. barbatus in two features: the 
main bundle of each seed-leaf commences its vascular rearrangements 
in the base of the blade before the lateral strands have joined on to it ; also, 
the protoxylem of each seed-leaf-trace becomes completely exarch during 
its passage down the short but well-marked cotyledonary tube. 
Dianthus arenarius , L., resembles D. barbatus very closely. 
Gypsophila Saxifraga , L. The third type of transition is followed, 
and the vascular rearrangements begin in the base of the seed-leaves 
on a level with the top of the cotyledonary tube. The main changes take 
place in the upper part of the hypocotyl as in D. barbatus. 
Saponaria cerastoides , Fisch. ex C. A. Mey. (Fig. 1, B), does not differ 
in any essential feature from Gypsophila Saxifraga , with the exception that 
a cotyledonary tube is not formed. 
