i92o] ARBER— TENDRILS 441 



of twisting of a region which , although now apical, seems in reality 

 to be part of the leaf-base, has been utilized in tendril formation. 

 It is interesting that Polygonatum includes both species with twisted 

 leaves and also species whose leaves have tendril apices resembling 

 those of Gloriosa. Similarly in Smilax the torsion capacity of the 

 petiole seems to have fulfilled itself on specialized lines in the pro- 

 duction of a climbing organ. 



It may be noted in passing that the blade of Smilax often con- 

 forms to a shape which is one of the most characteristic among 

 those adopted by the pseudo-lamina of monocotyledons, its outline 

 being entire and more or less ovate, with a base which is cordate 

 or somewhat sagittate (fig. 1). Forms of this type, as has been 

 pointed out in a previous paper (1), are not only known in 

 the Liliaceae, but recur in the Alismaceae, Pontederiaceae, Dios- 

 coreaceae, Araceae, and Orchidaceae. This list may now be 

 increased by the addition of Cyanastrum cordijolium Oliver, of the 

 Haemodoraceae* and certain species of Commelina among the 

 Commelinaceae. 



- 



To the writer, the whole organization of the leaf of Smilax 

 is best explained according to the phyllode theory, and the inter- 

 pretation suggested has been reached from this standpoint. At the 

 same time, however, the view here propounded, of the origin of the 

 tendrils of this genus through chorisis of the petiole, in no way 

 depends upon this general theory. There is nothing to prevent 

 its independent acceptance by those w T ho do not share the conviction 

 that the leaves of monocotyledons are invariably of the nature of 

 petiolar or leaf-base phyllodes. 



Summary 



In this paper the conflicting views hitherto held regarding the 

 nature of the tendrils of Smilax are briefly considered, and it is 

 concluded, on grounds of anatomy and external morphology, that 

 these tendrils are equivalent to the petiole in morphological value, 

 and have arisen through chorisis or dedoublement of that organ. 



Balfour Laboratory 

 Cambridge, England 



