Ouar. XV. ON THE DROSERACEA. 359 
power.* We are thus led to inquire how the so-called 
tentacles of Drosera, which are manifestly of the same 
general nature as the glandular hairs of the above 
three genera, could have acquired the power of moving. 
Many botanists maintain that these tentacles consist 
of prolongations of the leaf, because they include vas- 
cular tissue, but this can no longer be considered as a 
trustworthy distinction.t The possession of the power 
of movement on excitement would have been safer 
evidence. But when we consider the vast number of 
the tentacles on both surfaces of the leaves of Droso- 
phyllum, and on the upper surface of the leaves of 
Drosera, it seems scarcely possible that each tentacle 
could have aboriginally existed as a prolongation of 
the leaf. Roridula, perhaps, shows us how we may 
reconcile these difficulties with respect to the homo- 
logical nature of the tentacles. The lateral divisions 
of the leaves of this plant terminate in long tentacles ; 
and these include spiral vessels which extend for only 
a short distance up them, with no line of demarcation 
between what is plainly the prolongation of the leaf 
and the pedicel of a glandular hair. Therefore there 
would be nothing anomalous or unusual in the basal 
parts of these tentacles, which correspond with the 
marginal ones of Drosera, acquiring the power of 
movement; and we know that in Drosera it is only 
the lower part which becomes inflected. But in order 
to understand how in this latter genus not only the mar- 
ginal but all the inner tentacles have become capable 
of movement, we must further assume, either that 
through the principle of correlated development this 
* Sachs, ‘ Traité de Botanique” hague, 1873, p. 6. ‘Extrait des 
3rd edit. 1874, p. 1026. Videnskabelige Meddelelser de 
¢ Dr. Warming. ‘Sur la Diffé- la soc. d’ Hist. nat. de Copen 
ence entre les Trichomes,’ Copen- _hague,’ Nos. 10-12, 1872, 
24 
