292 CONCLUDING REMARKS [Chap. XV. 



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 the 

 genera, being replaced in Koridula by hairs, and in most 

 species of Drosera by absorbent papillae. Drosera binata, 

 with its linear and bifurcating leaves, is in an intermediate 

 condition. It still bears some sessile glands on both surfaces 

 of the leaves, and on the lower surface a few irr^rularly 

 placed tentacles, which are incapable of movement. A 

 further slight change would convert the linear leaves of this 

 latter species into the oblong leaves of Drosera anglica, and 

 these might easily pass into orbicular ones with footstalks 

 like those of Drosera rotundifolia. The footstalks of this 

 latter species bear multicellular hairs, which we have good 

 reason to believe represent aborted tentacles. 



The parent form of Dionaja and Aldrovanda seems to 

 have been closely allied to Drosera, and to have had rounded 

 leaves, supported on distinct footstalks, and furnished with 

 tentacles all round the circumference, with other tentacles 

 and sessile glands on the upper surface. I think so because 

 the marginal spikes of Dionaja apparently represent the ex- 

 treme marginal tentacles of Drosera, the six (sometimes 

 eight) sensitive filaments on the upper surface, as well aa 

 the more numerous ones in Aldrovanda, representing the 

 central tentacles of Drosera, with their glands aborted, but 

 their sensitiveness retained. Under this point of view we 

 should bear in mind that the summits of the tentacles of 

 Drosera, close beneath the glands, are sensitive. 



The three most remarkable characters possessed by the- 

 sereral members of the Droseracete consist in the leaves of 

 some having the p)ower of movement when excited, in their 

 glands secreting a fluid which digests animal matter, and in 

 their absorption of the digested matter. Can any light be 

 thrown on the steps by which these remarkable powers were 

 gradually acquired? 



As the walls of the cells are necessarily permeable to 

 fluids, in order to allow the glands to secrete, it is not 



