THE SEEDLING AND YOUNG PLANT 49 
If we now trace the vascular bundles of the leaf- 
trace in the other direction—that is, up into the leaf—- 
their course is simple enough, as shown in figs. 10 and 
11. The five bundles run through the midrib and the 
stronger lateral ribs to the tips and edges of the leaf, 
first breaking up into several strands in the petiole and 
midrib, and then becoming finer and finer as they give 
off the lateral strands. The median bundle does little 
more than run directly through the leaf as the midrib, 
becoming finer and finer as it nears the apex. The 
two lateral median bundles behave in a somewhat 
curious way. We have already seen how large and flat 
they are at the leaf insertion (fig.10). Soon after enter- 
ing the petiole they break up into several strands, two 
of which converge and take a course along the dorsal 
side of the midrib, thus nearly completing a cylinder of 
bundles enclosing a pith ; moreover, the xylem portions 
of these bundles are all turned inwards towards the pith. 
The lateral bundles, coming obliquely into the leaf 
insertion, pass up the midrib side by side with the 
above, and, like them, break up into parallel strands. 
Before entering the midrib they give off small bundles 
(fst in fig. 10) to the pair of minute stipules which flank 
the petiole. As the strands pass along the midribs and 
chief lateral ribs they interosculate in various degrees, 
and give off smaller side branches into the mesophyll 
of the leaf (see Chapter VI.). 
The veins which spring from the chief lateral ribs 
run towards one another and anastomose, giving off 
E 
