Cuap. V. CONCLUDING REMARES. 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 haying this power and habit. 
For the internodes 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 Cucurbitacee, Passi- 
floracese, and Vitacee. In the first, the internodes 
revolve; but I have heard of no twining form, with 
the exception (according to Palm, p. 29. 52) of Momor- 
dica balsamina, and this is only an imperfect twiner. 
In the two other families I can hear of no twiners; 
and the internodes rarely have the power of revolving, 
this power being confined to the tendrils. 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- 
