Chap. V. CONCLUDING REMARKS. 191 



quently became capable of grasping a support ; and this, 

 as we shall presently see, is a great additional advantage. 



From analogous reasons, it is probable that all 

 tendril-bearers were primordially twiners, that is, are 

 the descendants of plants having this power and habit. 

 For the intemodes of the majority revolve ; and, in a 

 few species, the flexible stem still retains the capacity 

 of spirally twining round an upright stick. Tendril- 

 bearers have undergone much more modification than 

 leaf-climbers; hence it is not surprising that their 

 supposed primordial habits of revolving and twining 

 have been more frequently lost or modified than in 

 the case of leaf-climbers; The three great tendril- 

 bearing families in which this loss has occurred in the 

 most marked manner, are the Cucurbitaceee, Passi- 

 floracese, and Vitacese. In the first, the intemodes 

 revolve; but I have heard of no twining form, with 

 the exception (according to Palm, p. 29. 52) of Momor- 

 dica lalsamina, and this is only an imperfect twiner. 

 In the two other families I can hear of no twiners; 

 and the intemodes rarely have the power of revolving, 

 this power being confined to the tendrUs. The inter- 

 nodes, however, of Passiflora gracilis have the power 

 in a perfect manner, and those of the common Vine in 

 an imperfect degree: so that at least a trace of the 

 supposed primordial habit has been retained by some 

 members of all the larger tendril-bearing groups. 



On the view here given, it may be asked. Why have 

 the species which were aboriginally twiners been con- 

 verted in so many groups into leaf-climbers or tendril- 



