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portion of all tropical and extra-tropical plants. In Persoon's Synopsis it is as 

 1 to 2 ; and since the publication of that work, the knowledge of tropical has 

 been enlarged in a greater proportion than that of extra-tropical plants. Al- 

 though, however, the quotients in the torrid and temperate zones may be nearly 

 equal upon the whole, when taken in subdivisions there will be an inequality. 

 In the warm regions of South America, the Grasses, under 200 toises eleva- 

 tion, form from l-15th to l-16th of the whole ; in the West Indies l-17th ; on 

 the river Essequibo, in Guyana, l-12th to l-15th ; on the river Congo l-12th 

 to l-13th ; in Guyana 1-1 0th ; (in the last three the local circumstances are 

 peculiarly favourable for the Grasses) ; in the East Indies according to Brown, 

 l-12th; in Arabia l-15th ; and in tropical New Holland l-10th to 1-llth. 

 Now, attending to the circumstance, that tropical are scarcely so well known 

 as other phanerogamic plants, it is not improbable that the true quotient for 

 the torrid zone is l-10th to l-12th. In the warmer parts of the temperate 

 zone the Grasses appear to form a smaller proportion of the vegetation ; for, 

 in the extra-tropical parts of New Holland, they form from l-24th to 1 25th, at 

 the Cape l-35th, in Greece l-15th to l-16th, in the Canary Islands l-12thto 

 l-13th, in the Crimea and Caucasus l-14th to l-15th, in Naples 1-llth to 

 1-1 2th, in France l-13th, and in Egypt (where, however, the circumstauces 

 are peculiarly favourable) 1-lSth. Farther north the relative numbers seem to 

 rise somewhat higher ; in Germany l-13th, in Great Eritian 1-llth to l-12th, 

 in Denmark l-10th to 1-llth, in Scandinavia l-10th to 1-llth, in Kamchatka 

 l-7th to l-8th, Lapland 1-lOth, Iceland, l-8th to l-9th, Greenland 1 -8th to 

 l-9th, and in North America, according to Pursh, 1-I4th to l-15th. We may 

 assume, perhaps, as a medium for the warmer parts of the temperate zone, 

 l-12th to l-14th : for the colder, together with the polar regions, l-8th to 

 l-10th. That almost in every Flora the quotient is considerably higher than 

 in the works of Persoon, and of RSmer and Schultes, affords another proof, 

 that, in the rule, the distribution of the Grasses is more extensive than that of 

 the other phanerogamic plants. 



"In southern Europe the number of the Grasses seems to diminish according 

 to the elevation, for in the Alpine Flora they are only l-18th. Their distribution 

 according to elevation does not, therefore, accord with that of the latitude ; in 

 South America the agreement is greater, for the relative numbers are, to 200 

 toises, l-15thto l-16th; 200 to 1100 toises, l-15th to l-16th; 1100 to 1600 

 toises, 1-llth; above 1600 toises, l-14th. 



" A detailed representation of the distribution of the cultivated Gramina 

 would certainly be very interesting. Here we must restrict ourselves to a short 

 and general outline, We shall endeavour to specify those Gramina which are 

 the prevailing ones in the large zones and continents, mentioning, in passing 

 those plants of other families which either supply the place of, or are associated 

 with, the different lands of grain, as the chief article of food. This distribu- 

 tion is determined not merely by climate, but depends on the civilization, in- 

 dustry, and traffic of the people, and often on historical events. 



" Within the northern polar circle, agriculture is found only in a few places. 

 In Siberia grain reaches at the utmost only to 60°, in the eastern parts scarcely 

 above 55°, and in Kamchatka there is no agriculture even in the most southern 

 parts (51°). The polar limit of agriculture on the northwest coast of Ame- 

 rica appears to be somewhat higher ; for, in the more southern Russian posses- 

 sions (57° to 58°), barley and rye come to maturity. On the east coast of 

 America it is scarcely above 50° to 52°. Only in Europe, namely, in Lapland, 

 does the polar limit reach an unusually high latitude (70°). Beyond this, 

 dried fish, and here and there potatoes, supply the place of grain. 



" The grains which extend farthest to the north in Europe are barley and 

 oats. These, which in the milder climates are not used for bread, afford to the 



