THE MORPHOLOGICAL COMPOSITION OF PLANTS. 



31 



bear 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 will 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, will further enforce this 

 conclusion. 



Here we may advantageously note, too, how in such cases, 

 the leaf-stalk 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 ; 



