735 
Seedling Anatomy of Certain Sympetalae . 
At the base of the lamina, often only a single bundle is present. In 
this strand, rearrangements begin in the upper part of the petiole, by the 
disappearance of the phloem elements from the sides simultaneously with 
the lateral elongation of the xylem. Almost immediately the lower (‘ ex- 
ternal ') phloem bifurcates, and traverses the remaining part of the petiole 
and the hypocotyl as two distinct groups (Diagram 5, Fig. %). 
In some cases the rearrangement of the xylem results in the production 
of three masses — a small median strand of protoxylem, and two lateral 
strands consisting chiefly of metaxylem, in which protoxylem elements can 
be distinguished for some distance. Even in the clearest cases, these 
Diagram 5. Datura Stramonium. 
lateral protoxylem groups disappear after a longer or a shorter course, while 
in other examples the only definite protoxylem is the median one. The 
lateral xylem groups diverge, and take with them the corresponding external 
phloem mass and also part of the internal phloem, and further rearrange- 
ment in the upper region of the hypocotyl results in the production of the 
structure shown in Diagram 5, Fig. 3. 
Further changes are due to the closing in of the various tissues. Each 
external phloem mass joins its fellow from the opposite cotyledon ; the 
whole of the xylem derived from each cotyledonary bundle moves towards 
the centre of the hypocotyl, and at the same time the metaxylem strands 
of each bundle fuse and take up a position internal to their respective proto- 
xylems (Diagram 4, Fig. 4). Finally, the two xylem bundles meet at the 
centre, and a typical diarch plate results (Diagram 4, Fig. 5). 
