TLIE WALLFLOWER 40 



position to the five projecting ridges seen on the 

 surface of the stem. It is most convenient to follow 

 the bundle from above downwards. It enters the stem 

 from the midrib of the leaf, runs inwards for a short 

 distance, and then turns straight downwards, continuing 

 its descending course in the stem through five inter- 

 nodes. It then reaches the leaf vertically below that 

 from which it started, and joins on to its bundle. 

 Besides the principal bundle, two smaller lateral 

 bundles enter the stem from each leaf, and these 

 behave in the same way. Hence in any transverse 

 section of the stem we cut through about fifteen 

 bundles, five principal ones, each representing the 

 middle bundle of a leaf, and ten smaller ones, forming 

 the continuation of the lateral leaf - bundles. The 

 number is not always exact, for the smaller bundles 

 may branch or unite together on their downward 

 course. It is quite easy to understand the arrange- 

 ment if we bear in mind that each ridge on the outside 

 of the stem corresponds to a principal bundle, which 

 is accompanied by its two smaller side bundles. At 

 the insertion of each leaf the various bundles are 

 connected together by cross branches. 



The description given applies, with slight variations 

 in detail, to the whole stem of the Wallflower, with the 

 exception of the first few internodes of the seedling. 

 These have a simpler arrangement of the leaves, and 

 consequently a smaller number of bundles. The 

 section (Fig. 20) is taken from one of these first- 

 formed and simpler internodes. 



Vascular bundles of this kind, which are continuous 

 4 



