358 CONCLUDING REMARKS Cuar. 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 
Dionza, 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 Dionewa 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, 
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 Roridula 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 known of a trichome haying such 
