Structure of Acer Pseudoplatanus. 585 
insertion of the six bundles from the leaves arising at that node (Fig. 41). 
The half-bundles so produced move apart and unite with the bundles enter¬ 
ing the stem at the previous node. The bifurcation of the midrib bundles is 
always somewhat precocious compared with that of the laterals (Figs. 4J, 60), 
this admitting of the insertion, on the adjacent faces of the two half-bundles, 
of the strands representing the vascular supply of the axillary buds. The 
six bundles entering the epicotyl at the first epicotyledonary node only 
traverse a single internode before entering the hypocotyl. The laterals 
unite with the diagonally placed cotyledonary metaxylems without bifurca¬ 
tion, whilst the midrib, as has been stated previously, generally bifurcates, its 
halves behaving similarly. The six strands from the second epicotyledonary 
node are also involved in the bundle fusions occurring at the apex of the 
hypocotyl. Of these the midribs bifurcate in the usual way, but become 
joined to the laterals from the node below a little earlier than is generally 
the case. No division of the laterals has been detected, but they appear to 
move outwards with the half-bundles of the midribs of the first epicotyle¬ 
donary node and so link with the cotyledonary strands. It is, however, 
somewhat difficult to determine their exact fate, since by the time that they 
are sufficiently differentiated in this region the limits of the individual 
bundles are obliterated by secondary thickening. 
Abnormalities. 
Of the fifty-three seedlings examined, nine show some degree of depar¬ 
ture from the normal in the behaviour of their vascular strands during 
transition and are best dealt with individually. With two exceptions they 
may be arranged in two groups. In the first of these the abormality is 
generally the result of the persistence of plumular contributions, chiefly 
phloem, beyond the upper part of the hypocotyl and in some cases down 
into the root. It is not always possible, however, to refer the abnormality 
to plumular strands (e. g. in seedlings E and H below). 
In the second group the abnormality takes the form of the development 
of accessory groups of metaxylem in the root, which may or may not give 
rise to additional root poles. 
Group 1. 
Seedling A. This is a very young seedling in which the plumular 
elements are not well differentiated. A single phloem group appears in the 
intercotyledonary plane of one side and after persisting for some time 
dies out. 
Seedling B. This is also very young and is characterized by two groups 
of phloem in the intercotyledonary plane on opposite sides of the stele, one 
of these developing at a lower level than the other. Both persist to the 
