MORPHOLOGY 



25 



tions are furnished by liuscus aculeatus (Fig. 25), a small shrub whose 

 stems bear in the axils of their scale-like leaves (/) broad, sharp-pointed 

 cladodes (cl), which have altogether the appearance of leaves. The 

 flowers arise from the upper surface of these cladodes, in the axils of 

 scale leaves. In like manner the stems of the Opuntias (Fig. 26) are 

 considerably flattened, while the leaves are reduced to small thorny 

 protuberances. In this case the juicy flat shoots perform not only the 

 functions of assimilatory organs, but also serve as water-reservoirs in 

 time of drought. It is possible that all the leaves of a plant may 

 become more or less completely reduced, without any marked change 



Fig. 25. — Twig of Ruscus aculeatus. /,Leaf; 

 rf, cladode ; U, flower. (Nat. size.) 



Fig. 20. — Opuntia monacantha Haw. , showing flower 

 and fruit. (After Schumann, ^ nat. size.) 



occurring in the appearance of the stems, except that they then take 

 on a green colour ; this, for example, is the case in the Scotch Broom 

 (Spartium scojxcriimi), which develops only a few quickly-falling leaves 

 at the end of its long, naked twigs ; or, as in many species of rushes 

 (Juncus, Scirpus), whose erect, slender, wand-like stems are entirely 

 leafless and at the same time unbranched. As a rule, however, all 

 leafless green Phanerogams will be found to have swollen stems, as in 

 the variously shaped Euphorbiae and Cacti. 



A great reduction in the leaves, and also in the stems, often 

 occurs in phanerogamic parasites, in consequence of their parasitic 

 mode of life. The leaves of the Dodder (Cuscuta, Fig. 185, b) are 

 only represented by very small, yellowish scales, and the stem is 

 similarly yellow instead of green. The green colour would, in fact, 



