- 188 ROOT-CLIMBERS. Cuar. 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 aromatica emits aérial 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 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 Miller informs me aérial roots of a Philodendron 
that he saw in the forests of 
South 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 stems 
of twining plants which were thus 
ascending the trees; buthe after- 
wards found that they were the 
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 aérial roots of some other 
species of Philodendron hang 
vertically downwards, sometimes 
for a length of more than fifty feet. 
