GEOGRAPHY OF PLANTS. 275 



The Primuleae are almost the only plants that are common 

 to the frigid and to the temperate zone. The Contortae be- 

 long to the tropical region, where they form from tlie fortictli 

 to the fiftieth part of the whole. In the temperate zone they 

 diminish in number, until, towards the polar circle, they al- 

 most entirely cease. 



401. 



It is interesting also to know the limits within which the 

 cultivation of the useful plants is confined. The cultivation 

 of Cocoa, Coffee, Anatto, Cloves, and Ginger, is limited to 

 inter- tropical regions. The Sugar Cane, Indian Figs, Dates, 

 Indigo, and Battatas, pass the tropics as far as the 40di de- 

 gree of N. Lat. Cotton, Rice, Olives, Figs, Pomegranates, 

 Agrumse, and Myrtles, gi*ow in the open air, as far as the 

 45th and 4Gth degree. The Vine succeeds best with us 

 within the 50th degree of N. Lat. ; this, also, is the limit, es- 

 pecially in the West of Europe, of the cultivation of ]\Iaize, 

 Chesnuts, and Almonds. Melons also succeed to the same 

 latitude in the open air. 



In the West of Europe, the cultivation of Plums, Peaches, 

 Wheat, Flax, Tobacco, and Gourds, ceases at the 60th de- 

 gree of N. Lat. In the East of Europe, the cultivation of 

 Apples, Pears, Plums, and Cherries, terminates at the 57th 

 degree ; but Hops, Tobacco, Flax, Hemp, Buckwheat, and 

 Pease, succeed there even under the 60th degree. Hemp, 

 Oats, Barley, Rye, and Potatoes, are planted by the Nor- 

 wegians under the polar circle; and the Strawberry flourish- 

 es, even at the North Cape, under the 68th degree. 



S 2 



