CLIMBING PLANTS 37 



the clasping part of a tendril often becomes hard and rigid, the 

 portion between this and the plant may remain green and flexible. 

 Tliis latter portion also frequently forms a new spiral in the opposite 

 direction, thus rendering the connexion between the j^lant and its 

 support so supple and elastic that no damage is Hkely to accrue 

 from the motions caused by the wind. 



The tendrils which form long spirals are generally modified stems 

 or leaves, or they may be elongated leaflets of a compound leaf. 

 Those which are modified stems may be distinguished by their 

 growth from the axils of the leaves, denoting that they had their 

 origin in axillary buds after the manner of branches generally ; and 

 also, sometimes, by the fact that they bear imperfect leaves in the 

 form of Uttle scales. The tendrils of the Common or White Bryony 

 (p. 96) are of this nature ; while those of the Grape Vine are either 

 modified floral stems or altered flower-stalks. 



In some cases the entire leaf may be changed into a tendril, 

 in which instance its true nature is revealed by the presence of a 

 bud in its axil, as in many ordinary foHage leaves. More frequently, 

 however, the ' leaf-tendi'il ' is an altered leaflet of a compound 

 leaf, such as we see in the Peas and Vetches ; and it is interesting 

 to note in such cases that the loss entailed by the conversion of 

 leaflets into tendrils is often compensated for by the formation 

 of leaf -like stipules which are capable of performing the function of 

 leaves. In fact, we often find that the size of the stipules is pro- 

 portional to the number of tendrils produced ; and that when the 

 leaflets are considerably reduced in number by their conversion 

 into tendrils, not only are the stipules large and leafy, but the stem 

 itself may be extended laterally into broad wing-like expansions 

 which do the work of foliage leaves. 



Interesting illustrations of this are to be found in the Yellow 

 Vetch — a rather rare plant sometimes seen in sandy fields — in 

 which all the leaves are converted entirely into tendi'ils, and their 

 function performed by very large leafy stipules ; also in the Narrow- 

 leaved Everlasting Pea of bushy places, in which the leaflets of 

 the compound leaves are all converted into tendrils with the excep- 

 tion of two, the work of which is aided by the stipules and by the 

 ' wings ' of the stem and petioles. In the Rough-podded Vetch, 

 too, the stems and petioles are winged to serve the same end ; and 

 other British members of this genus have either large stipules or 

 winged stems, or both, to compensate for the loss of leaflets that 

 have been modified into tendrils. 



