CONCLUDING REMARKS. Ill 



parts acting as leaves or as flower-peduncles can have wholly 

 changed their function, and have come to serve as prehensile 

 organs. 



In the whole group of leaf-climbers abundant evidence has been 

 given that an organ, still subserving its proper function as a leaf, 

 may become sensitive to a touch, and thus grasp an adjoining ob- 

 ject. In several leaf-climbers true leaves spontaneously revolve ; 

 and their petioles, after clasping a support, grow thicker and 

 stronger. We thus see that true leaves may acquire all the lead- 

 ing and characteristic qualities of tendrils, namely, sensitiveness, 

 spontaneous movement, and subsequent thickening and indura- 

 tion. If their blades or lamina? were to abort, they would form 

 true tendrils. And of this process of abortion we have seen every 

 stage ; for in an ordinary tendril, as in that of the Pea, we ran 

 discover no trace of its primordial nature; in Mutisia clematis, 

 the tendril, in shape and colour, closely resembles a petiole with 

 the denuded midribs of its leaflets ; and occasionally vestiges of 

 lamina? are retained or reappear. Lastly, in four genera in the 

 same family of the Fumariacea? we see the whole gradation; for 

 the terminal leaflets of the leaf-climbing Fumaria qjjicinalis are not 

 smaller than the other leaflets ; those of the leaf-climbing Adhmia 

 cirrhosa are greatly reduced ; those of the Corydalis claviculata 

 (a plant which may indifferently be called a leaf-climber or tendril- 

 bearer) are either reduced to microscopical dimensions or have 

 their blades quite aborted, so that this plant is in an actual 

 state of transition ; and, finally, in the Dlcentra the tendrils are 

 perfectly characterized. Hence, if we were to see at the same 

 time all the progenitors of the Dicentra, we should almost cer- 

 tainly behold a series like that now exhibited by the above-named 

 four genera. In Tropaolum tricolorum we have another kind of 

 passage ; for the leaves which arc first formed on the young plant 

 are entirely destitute of lamina, and must be called tendrils, whilst 

 the later-formed leaves have well-developed lamina?. In all cases, 

 in the several, kinds of leaf-climbers and of tendril-bearers, the 

 acquirement of sensitiveness by the mid-ribs of the leaves appa- 

 rently stands in the closest relation with the abortion of their 

 lamina? or blades. 



On the view here given, leaf-climbers were primordially twiners, 

 and tendril-bearers (of the modified leaf division) were primor- 

 dially leaf-climbers. Hence leaf-climbers are intermediate in 

 nature beiween twiners and tendril-bearers, and ought to be 

 related to both. This is the case ; thus the several leaf-climbing 



