188 KOOT-OLIMBERS. Chap. V. 



Ivy, placed against glass, barely adhered to it, yet 

 secreted a little yeUowish matter. I may add, that the 

 rootlets of the Marcgravia dvhia can adhere firmly to 

 smooth painted wood. 



Vanilla aromaiica emits aerial roots a foot in length, 

 which point straight down to the ground. According 

 to Mohl (p. 49), these crawl into creyices, and when 

 they meet with a thin support, wind round it, as do 

 tendrils. A plant which I kept was young, and did 

 not form long roots ; but on placing thin sticks in 

 contact with them, they certainly bent a little to that 

 side, in the course of about a day, and adhered by 

 their rootlets to the wood; but they did not bend 

 quite round the sticks, and afterwards they re-pursued 

 their downward course. It is probable that these slight 

 movements of the roots are due to the quicker growth 

 of the side exposed to the light, in comparison with 

 the other side, and not because the roots are sensitive 

 to contact in the same manner as true tendrils. Ac- 

 cording to Mohl, the rootlets of certain species of 

 Lycopodium act as tendrils.* 



* Fritz Miiller informs me aerial roots of a Philodendron 



that he saw in the forests of which grew on the branches above. 



Siiuth Brazil numerous black These roots therefore seem to be 



strings, from, some lines to nearly true twiners, though they use 



an inch in diameter, winding tlieir powers to descend, initead of 



spirally round the trunks of gi- to ascend like twining plants', 



gantio trees. At first sight he The aerial roots of some other 



thought that they were the stems species of Philodendron hang 



of twining plants which were thus vertically downwards, sometimes 



ascending the trees ; but he after- for a length of more than fifty feet 

 wards found that they were the 



