198 



SCIENCE OF GARDENING. 



Part II. 



914. The temperature of summer, as it varies only by the intensity of heat, is not pro- 

 ductive of so many injurious accidents as that of spring. Very hot dry summers, however, 

 destroy many delicate plants, and especially those of cold climates. A very early summer 

 is injurious to the germination and progress of seeds ; a short summer to their ripening, 

 and the contrary. 



915. Autumn is an important season for vegetation, as it respects the ripening of seeds ; 

 hence where that season is cold and humid, annual plants, which naturally flower late, are 

 never abundant, as in the polar regions ; the effect is less injurious to perennial plants, 

 which generally flower earlier. Frosts early in autumn are as injurious as those which hap- 

 pen late in spring. The conclusion, from these considerations, obviously is, that temperate 

 climates are more favorable to vegetation than such as are either extremely cold or ex- 

 tremely hot. But the warmer climates, as Keith observes, are more favorable upon 

 the whole to vegetation than the colder, and that nearly in proportion to their distance from 

 the equator. The same plants, however, will grow in the same degree of latitude, 

 throughout all degrees of longitude, and also in correspondent latitudes on different sides 

 of the equator ; the same species of plants, as some of the palms and others, being found 

 in Japan, India, Arabia, the West Indies, and part of South America, which are all in 

 nearly the same latitudes ; and the same species being also found in Kamschatka, Ger- 

 many, Great Britain, and the coast of Labrador, which are all also in nearly the same lati- 

 tudes. ( Willdenow, p. 374.) 



916. The most retnarkable circumstances respecting the temperature in the three zones, is 

 exhibited in the following Table by Humboldt. The temperature is taken according to the 

 centigrade thermometer. The fathom is 6 French feet, or 6.39453 English feet. 



917. Elevation, or the height of the soil above the level of the sea, determines, in a very 

 marked manner, the habitation of plants. The temperature lessens in regular gradation, 

 in the same manner as it does in receding from the equator, and six hundred feet of ele- 

 vation, De Candolle states, are deemed equal to one degree of latitude, and occasion a 

 diminution of temperature equal to 23 of Fahrenheit ; 300 feet being nearly equal to half 

 a degree. Mountains 1000 fathoms in height, at 46 of latitude, have the mean temper- 

 ature of Lapland ; mountains of the same height between the tropics enjoy the tem- 

 perature of Sicily ; and the summits of the lofty mountains of the Andes, even where 

 situated almost directly under the equator, are covered with snow as eternal as that of the 

 north pole. 



