264 THE GEOGRAPHY 



4,000 species, and yet not twenty of them are cultivated 

 for the food of Man. In their real nature, these cultivated 

 Grasses are all summer plants, but varieties have been 

 obtained from some of the most important of them, which, 

 in the proper climate, sown in autumn, germinate and 

 pass the winter under the warm covering of snow, so that 

 they are in a condition to shoot out strongly in the spring, 

 while the soil is being prepared for the other summer plants. 

 Bearing in mind these exceptions, it may be said, that the 

 prosperity of all the Cerealia is dependant upon the tempe- 

 rature of the summer, or period of vegetation ; and if we 

 lay down their distribution on a map of the earth, it 

 exhibits a girdle which does not deviate so much from 

 the course of the Isotheral lines as many other conditions of 

 vegetation, 



But the conditions of temperature under which the 

 Corn-plants vegetate, may perhaps be more accurately 

 unfolded than is possible through a plan of the Isotheral 

 lines. In Egypt, on the banks of the Nile, Barley is sown 

 at the end of November, and harvested at the end of 

 February, the period of vegetation therefore amounts to 

 about ninety days, and the mean temperature of this season 

 is 69 48'. In Tuqueres, near to Cumbal, under the 

 equator, the time of sowing in the mountains, for Barley, 

 is about the 1st of June, the time of harvest, the 

 middle of November ; the mean temperature of this vege- 

 tating season of 168 days, is 50 12'. At Santa Fe 

 de Bogota they number 122 days between seed time 

 and harvest, with a mean temperature of 57 24'. 

 If now the number of days is multiplied by the 

 figures of the mean temperature, we obtain 6282 for 

 Egypt, 843311 for Tuqueres, for Santa Fe 648911, 

 therefore as nearly the same number as the uncer- 



