188 



ROOT-CLIMBERS. 



Chap. V. 



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

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

 rootlets of the Marcgravia dubia 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 crevices, 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 net 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 Muller informs me 

 that he saw in the forests of 

 Suuth Brazil numerous black 

 strings, from some lines to nearly 

 an inch in diameter, winding 

 spirally round the trunks of gi- 

 gantic trees. At first sight he 

 thought that they were the steins 

 of twining plants which were thus 

 ascending the trees; but he after- 

 wards found that they were the 



aerial roots of a Philodendron 

 which grew on the branches above. 

 These roots therefore seem to be 

 true twiners, though they use 

 their powers to descend, instead of 

 to ascend like twining plants. 

 The aerial roots of some other 

 species of Philodendron hang 

 vertically downwards, sometimes 

 for a length of more than fifty feet 



