THE MORPHOLOGICAL COMPOSITION OF PLANTS. 



31 



oear simple leaves in the midst of compound ones, the rela- 

 tive smallness of such simple leaves shows that the buds from 

 which they arose were ill-supplied with sap ; it wUl cease to 

 be doubted that a foliar organ may be metamorphosed into a 

 group of foliar organs, if furnished, at the right time, with 

 a quantity of matter greater than can be readily organized 

 round a single centre of growth. An examination of the 

 transitions through which a compound leaf passes into a 

 doubly-compound leaf, as seen in the various intermediate 

 forms of leaflets in Fig. 65, wlU further enforce this 

 conclusion. 



H ere we may advantageously note, too, how in such cases, 

 the leaf-staUc undergoes concomitant changes of structure. 

 In the bramble-leaves above described, it becomes compound 

 simultaneously with the leaf — the veins become mid-ribs while 

 the mid-ribs become petioles. Moreover, the secondary stalks, 

 and still more the main stalks, bear thorns similar in their 

 shapes, and approaching in their sizes, to those on the stem; 



