PETIOLE AS BLADE 



183 



the twig on which 

 it is borne, as it 

 is with all leaves, 

 but passes 

 through it. The 

 explanation of 

 these anomalies 

 will be found on 

 some of the shoots 

 which spring 

 from low down 

 on the trunk in 

 the deep shade of 

 the upper foliage,, 

 or from the stump 

 of a tree that has 

 been cut down. 

 There we find 

 bipinnate leaves 

 with small .leaf- 

 lets, and a broad 

 petiole that shows 

 exactly how the 

 upper * leaves * 

 have been 

 formed. We 



may find at every stage, leaves with several pairs of 

 pinnae and a slightly broadened petiole, to leaves with 

 broad petiole and only two small pinnae, and finally the 

 broad red petiole alone without leaflets (fig. 44). 



This broad petiole standing stiffly upright with its 

 plane vertical, thereby catches less of the sun when 



FIG. 43 

 ACACIA ARABICA, Willd. 



