235 
themselves to Vanilla leaves of the same or neighbouring plants ; 
but here, the stomata being small and narrow, the root hairs 
do not penetrate, the epidermis remains smooth, and the root 
is not nearly so firmly adherent as in the above case. The chief 
strength of the root tendril is due to the central vascular 
bundle, which contains a good deal of sclerenchyma and has a 
breaking strain when adult of about 4 kilo’s, that of the root 
as a whole being about ’/, kilo more. If firmly attached, the 
root tendril generally first breaks close to the attached coiling 
s—s sS—s A—P 
portion. Adult attached tendrils average 350 to 450 and 250 
to 300. 100th of a mm. in diameter. Contact produces only a 
slight thickening and a slight strengthening. The stem of 
Vanilla can support 15 kilo’s and breaks with from 18 to 20 
kilo’s. The weight of 3'/, meters of the stem of Vanilla, with 
the leaves and roots attached, was when fresh 600 grammes. A 
single attached root tendril can, therefore, at the utmost support 
: : x at 261/, meters, or allowing the usual factor 
7° 600 2 
of safety = 4'/, metres. 
The attached root-tendril remains radial in its internal struc- 
ture, a slight amount of collenchymatous thickening takes place 
in the cortex, and the sclerenchyma in the vascular bundle is 
somewhat more developed, than in the unattached root-tendril, 
which latter finally slowly withers and dies. 
The long “Nahrwurzeln” which grow downwards and strike 
root in the soil may be 1 to 2 metres in length above ground. 
They are only few in number and arise from the ventral sur- 
face of the stem between the short root-tendril and the base 
of the leaf. Whilst young and not more than 10 cm. long, they 
have hardly any geotropic or heliotropic irritability, but are 
sensitive to contact and may twine once or twice around a 
support or be deflected along it, forming root hairs especially 
if in a moist atmosphere, and flattening on the surface in 
contact. When older they possess distinct geotropic, and a 
much weaker aheliotropic irritability, but are nevertheless still 
