GEOGRAPHY OF PLANTS AND ANIMALS.- 355 



and the more so, as Ehrenberg, as I have already remarked, 

 has discovered that the nebulous dust or sand which mariners 

 often encounter in the vicinity of the Cape Verd islands, and 

 even at a distance of 380 geographical miles from the Afri- 

 can shore, contains the remains of eighteen species of sili- 

 ceous-shelled polygastric animalcules. 



Vital organisms, whose relations in space are comprised 

 under the head of the geography of plants and animals, may 

 be considered, either according to the difference and relative 

 numbers of the types, (their arrangement into genera and 

 species,) or according to the number of individuals of each 

 species on a given area. In the mode of life of plants, as in 

 that of animals, an important difference is noticed ; they either 

 exist in. an isolated state, or live in a social condition. Those 

 species of plants which I have termed social,* uniformly cover 

 vast extents of land. Among these we may reckon many of 

 the marine algae cladonia3 and mosses which extend over 

 the desert steppes of Northern Asia grasses, and cacti grow- 

 ing together like the pipes of an organ avicenniae and man- 

 groves in the tropics and forests of coniferae and of birches 

 in the plains of the Baltic and in Siberia. This mode of geo- 



mentum in Area fuisse omnia genera, si in insulis quo transire non possent, 

 multa animalia terra produxit." Augustinus, De Civitate Dei, lib. xvi. 

 cap. 7; Opera, ed, Monach. Ordinis S. Benedicti, t. vii., Venet. 1732, 

 p. 422. Two centuries before the time of the Bishop of Hippo, we find 

 by extracts from Trogus Pompeius, that the generatio primaria was 

 brought forward in connection with the earliest drying up of the ancient 

 world, and of the high table-land of Asia, precisely in the same manner 

 as the terraces of Paradise, in the theory of the great Linnaeus, and in 

 the visionary hypotheses entertained in the eighteenth century regarding 

 the fabled Atlantis : " Quod si omnes quondam terrse submersae profundo 

 fuerunt, profecto editissimam quamque partem decurrentibus aquis pri- 

 mum de tec tarn ; humillimo autem solo eandem aquam diutissime 

 immoratam, et quanto prior quaaque pars terrarum siccata sit, tanto 

 prius animalia generare coepisse. Porro Scythiam adeo editiorem omni- 

 bus terris esse ut cuncta flumina ibi nata in Maeotium, turn deinde in 

 Ponticum et uEgyptium mare decurrant." Justinus, lib. ii. cap. 1. The 

 erroneous supposition that the land of Scythia is an elevated table-land, 

 is so ancient, that we meet with it most clearly expressed in Hippocrates, 

 De jEre et Aquis, cap. 6, 96. Coray. " Scythia," says he, " consists of 

 high and naked plains, which, without being crowned with mountains, 

 ascend higher and higher towards the north." 



* Humboldt, Aphorismi ex Physiologia chemica plantarwm, in he 

 Flora Fribergensis subterranea, 1793, p. 178. 

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