THE SEEDLING- AND YOl'NG- PLANT 49 



If we now trace the vascular bundles of the leaf- 

 trace in the other direction that is, np 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 fiat 

 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 rnesophyll 

 of the leaf (see Chapter VI.). 



The veins which spring from the chief lateral ribs 

 run towards one another and anastomose, giving off 



E 



