268 VEGETABLE ORGANOGRAPHY. 



longation of the petiole, as in Lathyrus Aphaca; — 

 branched, when this prolongation bears lateral branches, 

 which probably represent the middle nerves of the unde- 

 veloped leaflets or lateral segments ; this structure is 

 frequent in Vicia. When the tendrils are long they 

 readily twine around neighbouring bodies, and serve to 

 support the plants ; but sometimes they are so short, as to 

 be unable to perform this office, and only exist as indi- 

 cations of the tendency of certain petioles to be thus 

 prolonged ; we see this in Orobus. Lastly, the petioles 

 of several Fumariaceae, although terminated by foliaceous 

 limbs, are frequently twisted at the point so as to act the 

 part, and have the appearance of tendrils. Those of 

 Clematis cirrhosa, and some other species, remain after 

 the destruction of the segments of their limb, and form 

 kinds of tendrils. 



We know but a very small number of examples of 

 Foliary tendrils, that is to say, of leaves thus pro- 

 longed ; and these examples also are not of true limbs, 

 but of foliaceous petioles devoid of the limb, and with 

 the nerves, straight or parallel at the base, converging at 

 the apex into a flexible filament; as in Flag ellaria Indica, 

 Gloriosa superba, and the upper leaves of Fritillaria 

 verticillata. If the filament, which proceeds from the 

 middle nerve of Nepenthes, and is afterwards prolonged 

 into a cup, can be considered a true tendril, it will ap- 

 proach this class. 



Stipulary tendrils are very rare, and even doubtful ; 

 we ought to refer, perhaps, to this class: — 1st. The 

 filaments which arise from the axils of the cotyledons 

 of Trapa, and along the base of its stem. 2d. The 

 tendrils of the Cucurbitaceas, which occupy the place of 

 a stipule, but are only on one side of the leaf. 



Petiolary glands are usually sessile, or nearly so, and 

 but little prolonged ; but it sometimes happens that they 



