Chap. XV.] ON THE DROSERACE^. 291 



cells, and the pedicels include a bundle of spiral vessels. 

 But in these three genera these organs do not possess any 

 power of movement, and there is no reason to doubt that 

 they are of the nature of hairs or trichomes. Although in 

 innumerable instances foliar organs move when excited, no 

 case is known of a trichome having such power.* We are 

 thus led to inquire how the so-called tentacles of Drosera, 

 which are manifestly of the same general nature as the glan- 

 dular 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 tentacles 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. Roridula, perhaps, shows us 

 how we may reconcile these diflSculties with respect to the 

 homological 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 anom- 

 alous or unusual in the basal parts of these tentacles, 

 which correspond with the marginal ones of Drosera, acquir- 

 ing 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 become 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 numerous points, so as to unite 

 with the hairs, thus forming the bases of the inner tentacles. 

 The above-named three genera, namely Drosophyllum, 



Snchs, Tralte de Botanique,' penhajrno. 1873, p. 0. ' Extrnit 



3rd edit. 1874, p. 1026. des Vldensknbellge Moddolelser 



' Dr. Warming. ' Sur la Dlf- de la Sop. d'HIst. nnt. de Copen- 



Wrence entre les Trichomes,' Co- hague,' Nos. 10-12, 1872. 

 20 



