198 



scip:nce of gardening. 



Part II. 



914. Tlie tempei'ature 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 tlieir ripening, 

 and the contrary. 



915. Autumn is an important season for vcgetatio!i, 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. Tlie 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 wanner 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 pl?jits, however, will grow in the same degree of latitude, 

 tliroughout all degrees of longitude, and also in correspondeiit latitudes on different sides 

 of the equator ; the same species of plants, as some of the pahiis and ethers, 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, wliich are all also in nearly the same lati- 

 tudes, (^jnildenoiv, -p. 374.) 



916. The jnost remarkable circumstances respecting the temperature in the three zones, is 

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

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





Torrid zone. 



Temperate zone. 



Frigid zone. 



Andes 

 of Quito, 

 Lat. 0°. 



Mountains 

 of Mexico, 

 Lat. 20°. 



Caucasus, 

 Lat. 421°. 



Pyrenees, 

 Lat. 42|». 



Alps, 

 Lat. 45i-^ to 

 46°. 



Lapland, 

 Lat. 67° to 

 70° 



Inferior limit of per- 1 

 petual snow - - 3 



2460 fa. 



2350 fa. 



1650 fa. 



1400 fa. 



1370 fa. 



550 fa. 



Mean annual heat at 1 

 that height - - ^ 











4°. 



6°. 



Mean heat of winter, do. 



If 









10°. 



20i°. 



Mean heat of Aug. do. 











6°. 



^2 • 



Distance between trees ) 

 and snow - - - ^ 



600 fa. 



350 fa. 



650 fa. 



230 fa. 



450 fa. 



300 fa. 



Upper limit of trees - 



1800 fa. 



2000 fa. 



1000 fa. 



1170 fa. 



920 fa. 



250 fa. 



Last species of trees to- ) 

 wards the snow - 3 



Escalonia 

 alstonia. 



Hnus 

 Occident. 



Betiila 

 alba. 



Pin. rubra 

 P. uncin. 



Pinus 

 abies. 



Betula 

 alba. 



Upper limit of the \ 

 Ericinese - ~ - ^ 



BefariaD, 

 1600 fa. 





Rhodod. 

 Caucas. 

 1380 fa. 





Rhodod. 

 ferrug. 

 11 70 fa. 



Rhodod. 

 laponic. 

 480 fa. 



Distance between the 7 

 snow and corn - - 5 



800 fa. 





630 fa. 





700 fa. 



1 



450 fa. 



- '» 



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

 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 covei-ed vrith snow as eternal as that of the 

 north pole. 



