GEOGRAPHY OF PLANTS. 53 



And as the proportions of these classes in the vegetable kingdom are as 83 

 to 1 7 per 1 00 species, the facts stated confirm the greater mean area of 

 monocotyledons over dicotyledons. 



A much shorter list is given of species having a very limited area, not 

 because such plants are less numerous — for the contrary is unquestionably 

 the fact — but because it is difficult to ascertain the exact limits occupied by 

 such species, except when they occur in very remote islands, or in countries 

 thoroughly explored by botanists. The island of St. Helena contains 

 several species, and even arborescent genera (of Composite), which are not 

 only found nowhere else, but which are confined to very small areas on the 

 island. The noble tree-fern, Dicksonia arborescens, occurs only on 

 the summit of Diana's Peak, the crown of the island. Kerguelin's Land 

 is the only known habitat for the genus Pringlea (Capt. Cook's cabbage) ; the 

 Auckland Islands, Tristan Da Cunha, Juan Fernandez, Madeira, and other 

 small islands, all contain species or genera peculiar to themselves. The 

 famous Cocos de Mer, or Double Cocoa nut (Lodoicea secliellarum), a 

 most remarkable and distinct genus of Palms, is only found at the rocky 

 islets of the Sechelles, and only inhabits a few of the group. In like manner, 

 each of the Canary Islands has species peculiar to itself; and this is still 

 more remarkable at the Gallapagos, of which group Dr. Hooker has pub- 

 lished an excellent flora (in the 20th vol. of Linn. Trans.). But limited 

 dispersion of species is not confined to remote islets. It occurs in con- 

 tinents. Several instances of extremely small areas of well marked species 

 occurring in Europe are given by M. de Candolle. To these we may add 

 a few exotic examples : — Dionoea muscipula, certainly a very remarkable 

 plant, not likely to escape the notice of American botanists, is limited to a 

 very small area in North Carolina (where it abounds), and a single station 

 in South Carolina. In like manner, the curious Cephalotus follicularis, 

 the Australian Pitcher Plant, which abounds in all the bogs round King 

 George's Sound, has been found nowhere else. The species, too, of 

 Nepenthes appear to be very local, each tropical island in the area 

 occupied by the genus having its peculiar kind. Disa grandijlora, the 

 most showy of terrestrial Orchideae, having a flower sometimes five inches 

 in breadth, with crimson petals, is only known on the borders of a little 

 streamlet on the summit of Table Mountain, at the Cape ; but along that 

 streamlet the plant is abundant. But many Orchideae, we suspect, have a 

 very limited extension. It is well known that the Cape flora is peculiarly 

 rich in species of Erica, upwards of 300 having been described. Several 

 of these are extremely local, while others are found scattered over many 



