DR. SCHLEIDEN S THEORY OF AGRICULTURE. 45 



currence of all those conditions on which the success of any par- 

 ticular species depends. In general the peculiar kinds under 

 cultivation in any given locality depend on the geographical dis- 

 tribution of the species. 



Every locality in the more anciently cultivated parts of the 

 Old World has some prevailing kind of bread-corn, that, viz. 

 which yields the greatest produce in that particular district. If 

 a line be drawn from the o6th degree of North latitude through 

 Asia, gradually approacliing the 60th degree passing through 

 the Lake of Ladoga, and then almost to tlie 66th degree in 

 Sweden — this line forms the southern limit of the first zone of 

 cultivation. Part of the mountainous distiicts of Korway and 

 Scotland belong to this zone. Korth of tliis line, as far as 

 cultivation extends towards the Pole, Barley, in some one of its 

 forms, is the peculiar bread-corn, and Rye is cultivated only in 

 favourable situations. A second line runs through Asia almost 

 coincident with the 51st degree, retiring in Russia and Germany 

 a little below 50°, proceeding through Holland and through the 

 north of England and Ireland. Between this and the former 

 line Rye is the staple corn, mixed here and there in favourable 

 localities with Wheat. Both these regions have besides a plant 

 of a different order producing Hour, especially in the northern 

 half of the Rye zone, viz., Buckw heat. In the south of England, 

 the north of France, the middle of Germany to the Alps, the 

 north of Turkey, the south of Russia, and from thence through 

 Asia in a broad zone to Persia and Thibet, AVheat is the bread- 

 corn, with Rye intermixed in rough mountainous districts. 

 Finally, the whole circuit of the Mediterranean Sea produces 

 Wheat and Maize almost in equal quantities. The environs of 

 the Red Sea, the nortli coast of the Indian Ocean, and the 

 north of India yield Wheat and Rice in pretty equal propor- 

 tions ; and finally in the two Indian Peninsulas, China, and Japan, 

 Rice is the exclusive staple. 



In all the northern districts the cereals are notoriously intro- 

 duced plants which would vanish entirely in all parts of Europe 

 at least, without cultivation. Their presence and their geogra- 

 phical distribution in those countries affirm nothing more than 

 that they have found there suitable conditions of climate. Even 

 supposing them to be indigenous, the cessation of their cultiva- 

 tion would cause them to disappear except from some very con- 

 fined district. The distribution of plants does not depend alone 

 on conditions of climate. We have in cultivation to provide cer- 

 tain conditions which nature has not provided in the field of our 

 exertions, w hile wild vegetation needs no such artificial help, since 

 plants in nature do not grow where the conditions necessary for 

 their existence are not present. 



