290 CONCLUDING REMARKS [Cuar, XV. 
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 vascular tissue, but this can no longer 
be considered as a trustworthy distinction.* The possession 
of the power of movement on excitement would have been 
safer evidence. But when we consider the vast number of 
the tenacles on both surfaces of the leaves of Drosophyllum, 
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. MRoridula, perhaps, 
shows us how we may reconcile these difficulties with respect 
to the homological nature of the tentacles. The lateral 
divisions of the leaves of this plant terminate in long ten- 
tacles; 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 marginal but all the inner tentacles have 
hecome capable of movement, we must further assume, either 
that through the principle of correlated development this 
power was transferred to the basal parts of the hairs, or that 
the surface of the leaf has been prolonged upwards at numer- 
ous points, so as to unite with the hairs, thus forming the 
bases of the inner tentacles. 
The above-named three genera, namely Drosophyllum, 
Roridula, and Byblis, which appear to have retained a 
primordial condition, still bear glandular hairs on both 
surfaces of their leaves; but those on the lower surface 
have since disappeared in the more highly developed genera, 
with the partial exception of one species, Drosera binata. 
The small sessile glands have also disappeared in some of 
* Dr. Warming, ‘Sur la Différence —_belige Meddelelser de la Soc. d’Hist. 
entre les Trichomes,’ Copenhague, nat. de Copenhague,’ Nos. 10-12, 
1873, p. 6. ‘Extrait des Videnska- 1872. 
