EOOT-CLIMBERS. 107 



rootlets of a plant which had grown up a plaistered wall. Attached 

 to two sets of rootlets on the same branch, I found very many 

 extremely thin threads of a transparent, not viscid, excessively 

 elastic substance, precisely like caoutchouc. These threads, at 

 one end, proceeded from the bark of the rootlet, and at the other 

 end were firmly attached to transparent particles of silex and other 

 hard substances. There could be no mistake in this observation, 

 for I played with the threads for a long time, under the microscope, 

 drawing them out with the dissecting-needles and letting them 

 spring back again. Tet, as I looked repeatedly at other rootlets, 

 similarly treated, and could never discover these elastic threads, 

 I infer tha.t the branch had probably been slightly moved from 

 the wall at some critical period, whilst the fluid secreted from the 

 rootlets was in the act of drying and of changing its nature 

 through the absorption of its watery parts. The genus Ficus 

 abounds with caoutchouc, and from the facts here given we may 

 infer that tliis substance, at first in solution and ultimately modi- 

 fied into an unelastic cement, is used by Fieus repens to cement 

 its rootlets to any object which it may ascend. Whether most 

 other plants, which climb by their rootlets, emit any cement I do 

 not know; but the rootlets of the Ivy, placed against glass, barely 

 adhered to it, yet secreted a little yellowish matter. I may add, 

 that the rootlets of Marcgravia duhia can adhere firmly to smooth 

 painted wood. 



Vanilla aromatica emits aerial roots a foot in length, which 

 point straight down to the ground. According to Mohl (S. 49), 

 these crawl into crevices, and, when they meet with a thin sup- 

 port, wind round it, like tendrils. A plant which I kept was 

 young, and did not form long roots ; but on placing thin sticks in 

 contact with tliem, they certainly bent, in the course of about a day, 

 a little to that side, and adhered by their rootlets to the wood ; 

 but they did not bend quite round the sticks, and afterwards they 

 repursued their downward course. If these rootlets are really 

 sensitive to contact and bend to the touched side, in this case 

 the class of root-climbers blends into tliat of tendril-bearers. 

 According to Mohl, the rootlets of certain species of Lycopodmrn 

 likewise act as tendrils. 



Concluding HemarJcs. 



reach 



' ' mi ^ ' 



the light, and to expose a large surface of leaves to its action 

 aud to that of the free air. This is effected by climbers with 



