218 THE FLORIST AND 



a tropical country, so rnuch as the little spot of cultivated land round a hut, 

 which shelters a very numerous Indian family. 



Not till long after did Man learn to know and cultivate the gifts of Ceres. 

 It must, in fact, surprise us, at present, to see that but a few species of a 

 single family of plants furnish the principal food of the greater proportion 

 of mankind, namely, the so-called Corn-plants or Cerealia, of the family of 

 Grasses. This family includes nearly 4,000 species, and yet not twenty of 

 them are cultivated for the food of Man. In their real nature, these culti- 

 vated 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 depend- 

 ent upon the temperature 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 tempe- 

 rature of this season is about 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 tem- 

 perature of this vegetating 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, 8483 § J for 

 Tuqueres, for Santa Fe 6489 |g, therefore, as nearly the same number as 

 the uncertainty in the estimate of the days, the accurate mean temperature 

 and the want of knowledge whether or not the same kind of Barley is cultiva- 

 ted in all the places, will allow us to expect. Similar results are obtained 

 for Wheat, Maize, the Potato, and other cultivated plants. We may express 

 these results thus : Every cultivated plant requires a certain quantity of 

 heat for its development, but it is the same thing whether this heat is dis- 

 tributed over a shorter or longer space of time, so that certain limits are 

 not exceeded ; for where the mean temperature sinks below 36° 24', or 



