MORPHOLOGY 



45 



morphosed leaf laminae ; in other instances, as in the case of the 

 Australian species of Acacia (Fig. 171, 7, 8, 9), it is the leaf petioles 

 which, becoming flattened and leaf-like in appearance, supply the place 

 of the undeveloped leaf-blades. Such a metamorphosed petiole is called 



FIG. 48. Portion of stem and leaf of the common Pua, 

 J'isum sativuin. *, Stem,; n, istipules ; b, leaflets of 

 the compound leaf; r, leaflets modified as tendrils ; , 

 floral shoot, (i nat. size.) 



Fie. i'.'. l.at/ii/nt-s .I 



*, Stem ; n, stipules ; 

 b, leaf-tendril. ( nat. 

 size.) 



a PHYLLODE, and, except that it is expanded perpendicularly, closely 



resembles a cladode. From the latter, however, it is morphologically 



different, for the one represents a metamorphosed petiole, the other a 



metamorphosed shoot. In accordance with 



this distinction phyllodes do riot, like cladodes, 



spring from the axils of leaves. Just as 



stems become modified into thorns (Fig. 30), 



by a similar metamorphosis leaves may be 



converted into LEAF THORNS. Whole leaves 



on the main axis of the Barberry (Berberis 



vulgaris) become thus transformed into thorns, 



usually three, but in their character of leaves 



still subtend axillary shoots provided with 



foliage leaves. By a similar metamorphosis, 



the two stipules of the leaves of the common 



Locust (Eobinia Psewlacacia) become modified 



into thorns, while the leaf lamina persists 



as a foliage leaf (Fig. 50). 



The Root 



The third primary member of the corruo- 

 phytic plant in its typical development as 



FIG. 50. Part of stem and com- 

 pound leaf of Sobinin Pseud- 

 ncacin. n, Stipules modified 

 into thorns : ;/, pulvinus. 

 (A nat. sixc.) 



an underground root 



presents less marked differences in external form than were shown by 



