858 CONCLUDING KEMAEKS Chap. XV. 



hear from Prof. Oliver) two species ; the former con- 

 fined to the western parts of the Cape of Good Hope, 

 and the latter to Australia. It is a strange fact that 

 Dionsea, 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 Dion?ea are more highly 

 differentiated than those of Drosera ; 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 

 degree 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, 

 Koridula, 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 Droso- 

 phyllum they further include spiral cells, and the pedi- 

 cels 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 ex- 

 cited, no case is kno^^n of a trichome having such 



