Structure of Acer Pseudop/aiauus . 583 
the four bundles so produced the two more centrally placed ones rotate and 
unite with small lateral strands which in turn join the midrib as in the 
previous type. The two distally situated bundles also rotate, but unite with 
strands farther from the midrib which contribute to the formation of the 
large laterals passing into the stem. An additional complication is intro¬ 
duced by the fact that irregularities occur, not only in any two petioles 
Figs. 50-5. Transverse sections of a petiole in the upper part of which three feebly developed 
medullary bundles occurred locally, but died out at a lower level without fusion. The one persisting 
longest (Fig. 51 a) was represented by phloem only for the greater part of its course. Figs. 54 and 
55 show the bundle fusions near the base of the petiole. Fig. 51 a x 750, the remainder x 20. 
constituting a pair, but even on opposite sides of the same petiole. Such 
a case is shown in Figs. 44-9, in which the adaxial bundle on the right 
behaves in the manner described under (b) above, whilst that on the left 
bifurcates and its halves behave in the manner described under (c), but with 
the further peculiarity that the two bundles to which they unite are in their 
turn produced by the bifurcation of a parent bundle (Figs. 46-9). 
A further irregularity is occasionally produced by the union of the 
whole of one of the adaxial bundles with a strand which forms part of the 
main basal lateral instead of its uniting with one supplementing the midrib 
(Fig. 58). Whatever the type of bundle fusion, the ultimate result is always 
