290 CONCLUDING REMARKS [Chap. XV. 



success may be attributed to its manner of catching insects. 

 It is a dominant form, for it is believed to include about 100 

 species,* which range in the Old World from the Arctic 

 regions to Southern India, to the Cape of Good Hope, Mada- 

 gascar, and Australia ; and in the New World from Canada 

 to Tierra del Fuego. In this respect it presents a marked 

 contrast with the five other genera, which appear to be fail- 

 ing groups. Dionsea includes only a single species, which is 

 confined to one district in Carolina. The three varieties or 

 closely allied species of Aldrovanda, like so many water- 

 plants, have a wide range from Central Europe to Bengal 

 and Australia. Drosophyllum includes only one species, 

 limited to Portugal and Morocco. Roridula and Byblis each 

 have (as I hear from Prof. Oliver) two species; the former 

 confined to the westei-n parts of the Cape of Good Hope, and 

 the latter to Australia. It is a strange fact that Dioncea, 

 which is one of the most beautifully adapted plants in the 

 vegetable kingdom, should apparently be on the high road 

 to extinction. This is all the more strange as the organs of 

 Dionaea are more highly differentiated than those of Dros- 

 era; its filaments serve exclusively as organs of touch, 

 the lobes for capturing insects, and the glands, when excited, 

 for secretion as well as for absorption ; whereas with Drosera 

 the glands serve all these purposes, and secrete without being 

 excited. 



By comparing the structure of the leaves, their d^ree of 

 complication, and their rudimentary parts in the six genera, 

 we are led to infer that their common parent form partook 

 of the characters of Drosophyllum, Roridula, and Byblis. 

 The leaves of this ancient form were almost certainly linear, 

 perhaps divided, and bore on their upper and lower surfaces 

 glands which had the power of secreting and absorbing. 

 Some of these glands were mounted on pedicels, and others 

 were almost sessile; the latter secreting only when stimu- 

 lated by the absorption of nitrogenous matter. In Byblis 

 the glands consist of a single layer of cells, supported on a 

 unicellular pedicel; in Koridula they have a more complex 

 structure, and are supported on pedicels formed of several 

 rows of cells; in Drosophyllum they further include spiral 



Bfnthnm nnd Hooker, ' (Jon- one Bpeeles having been de- 

 era I'lantanim.' Anstralln Ir the Borlbed from this country, as Pro- 

 metropolis of the genus, forty- fessor Oliver Informs me. 



