CHAP. XV. ON THE DROSERACE.E. 



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.! 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, ' Traite de Botanique,' ha^ue, 1873, p. 6. ' Extrait des 



3rd edit. 1874, p. 1026. Videnskabelige Meddelelser de 



t Dr. Wanning ' Sur la Diffe- la Soc. d' Hist. nat. de Copcn 



tencc cntro les Trichomes,' Copen- hague,' Nos. 10-12, 1872. 



24 



