Cuar. XV.] ON THE DROSERACE. 289 
Madagascar, 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 failing groups. Dionea 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 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 Dionsa 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 Drosophyllum they further include spiral 
cells, and the pedicels 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 excited, no 
case is known of a trichome having such power.* We are 
* Sachs, ‘Traité de Botanique,’ 5rd edit. 1874, p. 1026. 
U 
