120 



SPINES OE THOENS, AND TENDEILS. 



selves often become spiny by the hardening of their midrib or 

 primary veins, and the diminution or absence of parenchyma, as in 

 Astragalus massiliensis (fig. 235 r), where the midrib becomes spiny 

 after the fall of some of the leaflets ; in the Holly, where all the veins 

 are so ; and in the Barberry (fig. 236), where some of the leaves, ///, 

 are produced in the form of spiny branches, with scarcely any paren- 

 chyma. In place of producing a lamina or blade at its extremity, the 

 petiole sometimes terminates in a spine. Stipules are occasionally trans- 

 formed into spines, as in Eobinia pseudacacia (fig. 237 s s), and 

 such is also the case with the swelling or pulvinus at the base of the 

 leaf, as in Ribes Uva-crispa (fig. 238 c c c). Branches are sometimes 

 arrested in their progress at an early stage of their development, and 

 do not appear beyond the surface of the stem ; at other times, after 

 having grown to a considerable size, they undergo decay. In both 

 instances the lower part of the branch becomes embedded and 

 hardened among the woody layers of the stem, and forms a knot. 



Tendrils. — A leaf-bud is sometimes developed as a slender spiral 

 or twisted branch, called a tendril or cirrus (cirrus, a curl). TendiUs 

 have their homologues in various organs, such as stems, branches, leaves, 



stipules, buds, midribs, parts 

 of the flower, etc. When 

 tendrils occupy the place of 

 leaves, and appear as a con- 

 tinuation of the leaf-stalk, 

 they are called petiolary, as 

 in Lathyrus Aphaca, in which 

 the stipules perform the func- 

 tion of true leaves. In 

 Flagellaria indica, Gloriosa 

 superba, Anthericum cirrha- 

 tum, and Albuca cirrhata, 

 the midrib of the leaf ends 

 in a tendril ; and in Vetches, 

 the terminal leaflet, and some 

 of the lateral ones at the 

 extremity of their pinnate 

 leaves, are changed, so as to 

 form a branching tendril. 

 In the Passion-flower the 

 lateral buds are thus altered. 



Fig. 239. 



Kg. 289. Portion of a branch of the Vine (VUls vinifera). a'. First axis, terminated hy 

 a tendril or cirrus, i/, which assumes a lateral position, and bears a leaf, /'. From the axil 

 of this leaf a second axis, a", comes off, which seems to be a continuation of the first, and 

 is terminated also by a tendril, v", bearing a leaf, /". From the axil of this second leaf a 

 third axis, a'", arises, terminated by a tendril, v'", and bearing a leaf, /'", from the axil of 

 which a fourth axis, a"", arises. 



