234 
properties. Mont probably included both types in his *Wurzel- 
ranken”, for the “Haftwurzeln” of Vanilla aromatica are never 
a foot long, whilst Darwm evidently examined “Nahrwurzeln” 
only. For an investigation of these and kindred points, Vanilla 
aromatica. Swz, was selected as the most suitable subject for 
experimental study. 
Vanilla aromatica. 
The stem of Vanilla is radial in structure but of dorsiventral 
habit. The leaves arise alternately on the right and left sides, 
whilst the short petiole twists so that the inner dorsal surfa- 
ces of the leaves face towards the light. A single clasping root 
or root-tendril arises at each node on the under surface only. 
Occasionally, however, if the stem be erect, a clasping root arises 
from the dorsal surface as well. The clasping roots are short 
and stout, being from 16 to 20 cm. long and from 3 to 4mm. 
thick. When coiled tightly around a support the inner concave 
surface becomes quite flat, the tendril assuming a triangular 
to hemispherical outline in transverse section. On the convex 
surface, if not in contact with anything, any hairs present are 
lost and a thick brown cuticular exodermal layer develops. On 
the adpressed concave surface , a thick mat of simple unicellular 
| hairs; commonly with blunt, swollen or even dichotamized 
apices, develops. If closely coiled, the sides of the root tendril 
become by the interlacing of this hairy growth tightly adherent 
to one another and to the support. 
Similarly the roots can adhere to flat surfaces by forming 
closely adpressed weft of hairs almost resembling a cellular 
tissue, when sectionized. One such adhering to the under sur- 
face of a leaf supported a weight of '/, kilo, but broke away 
with '|, kilo. In transverse section the epidermis of the leaf was 
seen to be somewhat roughened and slightly papillate where it was 
in contact with the root, whilst some of the hairs had grow? 
~~ the large and widely open stomata. This is interesting as 
being an indication of how an epiphytic or clasping aerial root 
might be converted into a parasitic one. The roots often attach 
