660 DISTRIBUTION AS AFFECTED BY TEMPEEATUEE. 



conspire to influence the temperature of countries. Insular and coast 

 climates are more equable, from the effect of the sea in preventing the 

 atmosphere from being much heated during the day, and much cooled 

 during night. In the interior of vast continents the extremes of tem- 

 perature are often great. Winds have a powerful effect on climate. In 

 China, the north-east monsoon brings great cold in February. The 

 state of a country as regards forests has a decided effect on the tem- 

 perature. In different quarters, the nature of the exposure also, 

 whether to the east or west, north or south, and the intervention of 

 elevated ranges of mountains, materially affect the temperature. 



In determining the limits of distribution in the vegetable king- 

 dom, we must know the mean monthly and the mean daily temperar 

 ture during those periods when vegetation is active. We must ascertain 

 the number of days which a plant requires to produce successively its 

 leaves, flowers, and fruit, and we must estimate the mean temperature 

 during that period. The conditions which define the limits of a plant 

 require that we should know at what degree of temperature its vege- 

 tation begins and ends, and further, the sum of the mean temperatures 

 during that time. Adanson first stated, that by adding the mean tem- 

 perature of each day from the commencement of the year, it was found 

 that when the sum reached a certain figure the same phenomena of 

 vegetation were exhibited, such as leafiing and fiowering. ^Boussin- 

 gault afterwards promulgated the statement, that if we multiply the 

 number of days (the length of time the culture of a summer plant 

 endures) by the mean temperature of this time, the product wiU be the 

 same in all countries and in all years. Thus, if a plant, he says, has 

 taken 20 days to ripen its seeds from the period of flowering, and the 

 mean temperature during these 20 days has been 50°, it wUl be found 

 that the heat received by the plant has been 1000°. The same sum 

 may be given by a greater amount of heat during a smaller number of 

 days. Lucas says that at Arnstadt, which is 897'4 French feet above 

 the level of the sea, and has a mean temperature of 46°'6 F., winter 

 Eye requires an average temperature of 48°'l F. during 105 days, in 

 all 5048°, to bring it into flower; from the flowering to the ripening 

 53 days, with a mean temperature of 63°'4, in all 3360°'2 ; altogether 

 the duration of the vegetation of Eye amounts to 158 days, with a 

 mean temperature of 53°, the sum of this being 8466°'9. Again, win- 

 ter Wheat requires for flowering 129 days, with a mean temperature 

 of 50°' 6, in all 6527°'4 ; from flowering to ripening 53 days, with a 

 mean temperature of 63°, in all 3339°. The total duration of the 

 vegetation of Wheat is thus 182 days at Arnstadt, with a mean tem- 

 perature of 54°, which makes a total of 9828°. Wheat requires a 

 higher mean temperature than Eye to bring it into flower ; it there- 

 fore blossoms on an average 24 days later, and consumes 6527°"4 

 of heat, while Eye only requires 5048°. From the flowering to the 



