PEOCEEDINGS OF THE SCIENTIFIC SOCIETIES OF LONBON. 289 



that leaf-climbers simultaneously acquire both capacities, it seems 

 probable that they were at first revolvers and could thus climb, and 

 that subsequently they became capable of grasping a support. Prom 

 analogous reasons it is probable that tendril-bearing plants were pri- 

 mordially twiners, that is, that they are descendants of plants having 

 this power and habit ; for in the majority the intemodes revolve like 

 those of twining plants, and in a very few the flexible stem retains 

 the capacity of spirally twisting aroimd an upright stick. "With 

 some tendril-bearing plants the internodes have lost the revolving 

 power, which has passed into the tendrils. These tendril-bearers 

 have undergone much more modification than leaf-climbers : hence 

 it is not surprising that their supposed primordial revolving and 

 twining habits have been lost or modified more frequently than in leaf- 

 climbers. The three great tendril-bearing families in which this loss 

 has occurred in the most marked manner are the Cucurbitacese, 

 Passifloracse, and Yitaceae. There is abundant evidence in the whole 

 group of leaf-climbers that an organ still subserving its proper func- 

 tion as a leaf, may become sensitive to a touch, and thus grasp an 

 adjoining object. Thus true leaves may acquire all the leading and 

 characteristic qualities of tendrils, namely sensitiveness, spontaneous 

 movement, and subsequently thickening and induration. If their 

 blades or laminsD were to abort they would form true tendrils ; and 

 of this process of abortion every stage may be met with. Accord- 

 ing to these views, leaf-climbers were primordially twiners, and ten- 

 dril-bearers (of the modified leaf division) were primordially leaf- 

 climbers. Hence the latter stand between twiners and tendril- 

 bearers, and ought to be related to both. This proves to be the 

 case, for the several leaf-climbing species of the Antirrhineae, of 

 Solanum, of Coccidus, and of Gloriosa are related to other genera 

 in the same family, or even to other species in the same genus, which 

 are true twiners. On the other hand the leaf-climbing species of 

 Clematis are very closely allied to the tendril-bearing Naravelice, and 

 the TumariaceaD include closely allied genera which are leaf- 

 climbers and tendi'il-bearers. Lastly, one species of Bignonia is 

 both a leaf-climber and a tendril-bearer, and closely allied species are 

 twiners. Tendrils consisting of modified flower peduncles likewise 

 aff'ord many transitional states. The common Vine gives every 

 possible grade, from grandly developed tendrils to a bunch of flower- 

 buds bearing the single usual lateral flower-tendi4L Some tendrils 

 are thus foliar and some axial in their nature, and it might have been 



