THE SEASON "WHY. 315 



From the rising of the sun, unto the going down of the same, the Lord's name 

 is to be praised." PSAUI cxin. 



not widely apart from each other, is totally different, though under the same 

 parallels. 



1245. Some plants are entirely confined to one side of our planet. Tho 

 beautiful genus Erica, or heath, of which there are upwards of 300 species, 

 occurs with breaks over a narrow surface, extending from a high northern 

 latitude to the Cape of Good Hope. But the whole continent of America does 

 not contain a single native specimen ; nor has a Pcenia been found in it, except 

 a solitary one to the west of the Rocky Mountains. On the other hand, the New 

 World contains many families, as the Cacti, which are not found naturally in 

 the Old. 



1216. Some plants occur in a single specific locality, frequently a contracted 

 area, and nowhere else. The beautiful Dlsa grandlflora is limited to a spot on 

 the top of the Table Mountain at the Cape ; and the celebrated cedar of Leba- 

 n^n appears to be restricted in its spontaneous growth to the Syrian moun- 

 tains. The small island of St. Helena has an indigenous flora, with a few excep- 

 tions different from that of the rest of the globe. 



1247. Mountain chains of no great width very commonly divide a totally dis- 

 tinct botany. There is a marked difference in the vegetation of the Chilian and 

 opposite side of the Andes, though the climate as well as the soil is nearly the 

 same, and the difference of longitude very trifling. In North America, two com- 

 pletely different classes of vegetation appear on the two sides of the Rocky 

 Mountains. A variety of oaks, palms, magnolias, azaleas, and magnificent 

 rhododendrons occur on the eastern side, all of which are uukn own oil the 

 western, the region of the giant piue. 



1248. The distinct vegetatioti possessed by various parts of the globe, has led 

 to its division into botanical kingdoms or phy to-geographical regions, named in 

 general after the genera thac are either peculiar to them, or predominant in 

 them. The arrangement of M. Schouw. which is usually adopted, discriminates 

 twenty-five great provinces of characteristic vegetation upon the surface of the 

 earth. 



In constituting any portion of the globe into a phyto-geographical region, M. 

 Schouw has proceeded upon the following principles : 1. That at least one-half 

 of the species should be indigenous in it. 2. That a-quarter of the genera 

 should also be peculiar to it, or at least should have a decided maximum. 3. 

 That individual families of plants should either bo exclusively confined to the 

 region, or have their maxima there. 



1249. The phenomena of botanical geography, and the facts of geology, are 

 mutually illustrative. The existing dry laud having been upheaved above the 

 waters at different epochs, it may be reasonably inferred that each portion on 

 its emergence received a vegetable creation in harmony with its position. The 

 ultimate constitution of the general surface into different botanical kingdoms 

 would hence follow, each of which has preserved its primitive features, while 

 adjoining, and even far distant foci, have to some extent intermingled their 

 respective products, under control of the natural agencies of diffusion. 



1250. The agents that involuntarily officiate in the diffusion of vegetable pro- 

 ducts are the atmosphere, the waters, and many animals. 



1. The impulsion of the atmosphere in its calmest state, is quite sufficient to 

 transport to considerable distances seeds furnished with downy appendages ot 

 wingleta, aa it the case with many plants, with the minute porulas at 



