40 



MORPHOLOGICAL DEVELOPMENT. 



leaved plants in full growth bear simple leaves in the midst 

 of compound ones, the relative 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 



