Curvahcre of Tendrils. 393 
has reached a length of 3 cm. This unequal growth also 
accounts for the hooked-shape formation of the tip. The 
cup-shaped cavity seems to be confined to tendrils of Passi- 
floreae, and so far as the observation of the author extended, 
it has been found to subserve no mechanical or other use, 
although it is possible to imagine it might prevent to a slight 
extent the slipping of a tendril away from a support before 
a curvature had been formed. It is altogether probable on 
the other hand that this cup-shaped cavity is entirely a 
vestigial structure in the transformation of a leafy branch 
into a tendril ; a conclusion justified by the fact that I have, 
in several instances, found the walls of this cup extended into 
a leaf-like lamina. Similar structures were observed by von 
Mohl (XIII). This is in accordance with the conclusions of 
Russell (XIX) as to the morphology of the tendrils of the 
Passifloreae. ‘ En resume, la vrille des Passiflores represente 
un rameau axillaire modifie qui peut avoir a sa base plusieurs 
rameaux secondaires depourvus de feuilles axillantes. Celui 
qui represente la premiere ramification se developpe toujours, 
et peut donner, soit un rameau feuille remplacant le rameau 
axillaire transforme en vrille, soit un pedicelle floral, simple 
ou ramifie. Les autres qui n’existent que dans la region 
florifere deviennent des pedicelles floraux ou bien avortent en 
tout ou en partie/ 
While no attempt has been made to determine the changes 
in the tissue directly connected with the curvature alone of 
tendrils, yet much attention has been given to their general 
anatomy and to the alterations of structure consequent upon 
curvature and coiling. Penhallow has described the anatomy 
of the tendrils of Cucurbita maxima and C. Pepo , and of Vitis 
cordifolia (XVII) ; A. Fischer, the general structure of the 
tendrils of Cucurbitaceae (IV) ; and Otto Muller has devoted 
considerable attention to several species of the Cucurbitaceae 
(XIV). Worgitsky has recently made a comprehensive inves- 
tigation into the comparative value of the mechanical tissues 
and their arrangement in a large number of species re- 
presenting many genera (XXII) inclusive of Passiflora . 
D d 2 
