DIV. I 



MORPHOLOGY 



171 



A striking modification is exhibited by shoots which only 

 develop reduced leaves, while the stems become flat and leaf-like and 

 assume the functions of leaves. Such leaf-like shoots are called 

 CLADODES or PHYLLOCLADES, and GOEBEL proposes to distinguish 

 those flattened shoots which have limited growth and specially leaf- 

 like appearance as phylloclades, and to term other flattened axes 



cladodes. An instructive example of 

 such formations is furnished by Ruscus 

 aculeatus (Fig. 196), a small shrub of 

 the Mediterranean region whose stems 

 bear in the axils of their scale-like 

 leaves (/) broad sharp-pointed cladodes 

 (cl) which have altogether the appear- 

 ance of leaves. The flowers arise from 

 the upper surface of these cladodes, 

 in the axils of scale leaves. These 

 phylloclades afford a good example of 

 the analogy between organs. Their 

 appearance and functions are those 



Fio. 192. Acacia marginata, with vertically- 

 placed phyllodes. (From SCHIMPER'S Plant- 

 Geography.) 



Fio. 193. Transverse section of the leaf 

 of Capparis spinosa, var. aegyptiaca. 

 (x 40. SCHIMPER after VOLKENS.) 



of leaves, but the morphological features mentioned above show that 

 they are shoots. A leaf-like flattening of the massive stems which 

 thus form cladodes is met with in the well-known Opuntias (Fig. 

 197), the bases of the branches remaining narrow. 



The great development of sclerenchyma in the shoots of many 

 xerophytes is associated with the development of THORNS. Thus 

 spiny shoots, though not lacking in other regions, are characteristic 

 of many xerophytes of deserts and steppes. The thorns are lignified 



