MODIFIED LEAVES, ETC. 69 



Spinous processes are developed upon the petiole in the upper part 

 of the leaves of certain Palms (Plectocomia), and even on the surfaces of 

 some leaves, as in some varieties of Holly. 



True spines, however, are more frequently dependencies of the stem : 

 thus in the Gooseberry they are developed from the pulvimis, below the 

 base of the petiole. In the Black-thorn (Prumis spinosa) the spines are 

 real branches (fig. 118), as also are the spines of Gleditschia triacanthos 

 (fig. 119), and the principal spines of Furze (TJlex], in which, however, 

 the points of the leaves are spinous also. 



Fig. 118. 



Fig. 119. 



Fig. 118. Spinous branch of Prumis spinom (Black-thorn). 

 Fig. 119. Spinous branch of Gleditschia triacanthos. 



Prickles (aculei), properly so called, are sharp woody processes, 

 straight or curved, occurring upon stems, leaf-stalks, at the points 

 or on the margins, or upper surface of leaves. They are distin- 

 guished from true spines by their originating from the epidermis, 

 like hairs, glands, &c., and by having no connexion with the 

 internal woody substance of the stem or ribs of the leaves &c. 



Glands. This is perhaps the most convenient place to mention 

 the nodular or discoid glandular bodies that occur in connexion 

 with certain leaves, as on the petioles of Passiflora &c. They are 

 distinct in their nature from the epidermal glands before mentioned, 

 and considerable attention has been directed to them on morpho- 

 logical grounds ; hence they will be adverted to again in speaking 

 of the flower. 



Sect. 5. THE LEAF-BDD. 



The bud is a compound structure, composed of a solid conical 

 basis, or growing point, supporting a number of rudimentary 

 leaves. In the leaf -bud, or rudiment of a shoot, the conical base 

 represents the future stem, with its internodes as yet undeveloped ; 

 the scales are either entirely rudimentary leaves, or a portion of 



