36 



BOTANY 



PAKT I 



PHYLLODE, and, except that it is expanded perpendicularly, exactly 

 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 



Fig. 35. — Portion of stem and leaf of the common Pea, Pisum 

 sativum, s, ; Stein ; n, stipules ; &, leaflets of the compound 

 leaf; r, leaflets modified as tendrils; a, floral shoot. 

 (£ nat. size.) 



Fig. 36. — Laihyrus Aphaca. 

 s, Stem ; n t stipules ; 

 b, leaf-tendril. (£ nat. 

 size.) 



do not, like cladodes, spring from the axils of leaves. Just as stems 

 become modified into thorns (Fig. 28), 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 give rise to axillary shoots pro- 

 vided with foliage leaves. By a similar meta- 

 morphosis, the two stipules of the leaves of 

 the common Locust (Robinia Pseudacacia) 

 become modified into tborns, while the leaf 

 lamina persists as a foliage leaf (Fig. 37). In 

 addition to stem and leaf thorns, many plants 

 are provided with other outgrowths of similar 

 appearance, which are often wrongly called 

 thorns ; but as they have, in reality, an alto- 

 gether different morphological origin, they 

 are more correctly termed prickles. The 

 , prickles so characteristic of the Rose and 

 pound leaf of RoUnia Pseuda- Blackberry belong to the same category as 



cacia. 



stipules modified hairs, and in no way represent metamorphosed 



; g. leaf-cushion. , j. ,, , , , , T ., , . 



(i nat. size.) segments of the plant body. Like hairs, 



they are also superficial outgrowths (emer- 

 gences). They have no definite fixed relation to the external seg- 

 mentation of a plant, but arise from any part of its surface. 



