548 PHYSICAL GEOGRAPHY. 



an interesting statement respecting the plant vulgarly known by the name of the rose of 

 Jericho, Anaslatica Hierochuntina, growing in the arid wastes of Arabia and Palestine. 

 By the time it dies, owing to the great drought, its tissue has become almost woody ; its 

 branches fold over each other till the whole mass assumes the form of a ball ; its seed- 

 vessels have their valves tightly shut ; and the plant remains adhering to the ground by 

 a solitary branchless root. The wind, which always acts powerfully along the surface of 

 a sandy plain, uproots this dry ball, and rolls it along. If it chance to meet with a splash 

 of water during its constrained but necessary journey, it speedily imbibes the moisture, 

 which causes the branches to unfold, and the pericarps to burst ; and the seeds which 

 could not have germinated if they had fallen on the dry ground, now sow themselves 

 naturally in a moist soil, where they are able to grow, and where the young plant may 

 support itself. 



The number of known species of plants on the surface of the earth, mentioned by bota- 

 nists from the time of Theophrastus to the present day, is thus given, in a memoir on 

 geographical botany by Mr. Hinds,' who accompanied the late expedition of the Sulphur 

 round the world, under the command of Sir Edward Belcher : 



B. c. 300. Theophrastus ... 500 



A. n. 70. Pliny .... 1000 



1683. Bauhin - 6000 



D. 1762. Linnaeus ... 8800 

 1806. Persoon - - - 27,000 



1820. De Candolle - - - 56,000 



Lindley, in 1835, gave the number at 86,000; but, according to Mr. Hinds, at the pre- 

 sent time there are 89,000 species of plants described; and computing for countries 

 scarcely examined, or as yet wholly unexplored, he supposes the total aggregate of species 

 which vegetate on the earth to amount to about 133,000. This is an estimate which only 

 goes a little beyond a similar calculation of De Candolle ; and when we reflect that the 

 interior of Africa, of Australia, and of the great islands of Oceanica, have not been visited 

 by the geographer and the naturalist, the estimate will not be deemed extravagant. It 

 illustrates the variety which marks the vegetable kingdom, and the work which still 

 remains to be accomplished in the department of botanical discovery and description. 

 Plants divided according to their station, or the physical nature of the locality to which 

 they are adapted, are ranged by De Candolle in fifteen classes, to which two others have 

 been added by M. Bory de Saint Vincent. 



1. Maritime or saline plants. These are terrestrial plants which grow on the borders 

 of the sea, or of salt lakes ; as salicornia, or saltwort, salsola, or glasswort, which abound 

 on the shores of the Mediterranean, and are there generally burnt for soda, used in the 

 manufacture of glass, especially at Marseilles. 



2. Marine plants, as the fuci and many of the algce, which are plentiful in the seas 

 that wash the coasts of Great Britain, and are often attached to stones and rocks near 

 the shore. They are either buried in the ocean, or, situated above low-water mark, are 

 alternately immersed and exposed to the action of the atmosphere ; but none of them can 

 be made to vegetate apart from its waters. 



3. Aquatic plants, growing in fresh water ; as sagittaria, or arrowhead, potamogeton, 

 or pond-weed, nymph&a, or white water-lily. They occupy the beds of rivers, and vege- 

 tate in the midst of the running stream or in stagnant pools, being for the most part 

 wholly immersed. The holy /cvajuog, or Pythagorean bean of antiquity, belonged to this 

 genus, and is probably identical with the produce of the Nelumbium, a stately aquatic, 

 common in various parts of the east, especially in China, where the ponds are literally 

 mantled with its leaves and flowers. 



4. Marsh or swamp plants, living in ground which is generally submerged, but occa- 

 sionally dry ; as ranunculus aquatilis and sceleratus, or water and celery -leaved crowfoot, 

 polygonum amphibium, or amphibious persicaria. 



