56 



COURSE OF THE SAP. 



PT. II. 



its leaves later directly as warmth, but it will ripen its 

 fruit earlier directly as the warmth of the climate. 

 Evergreens shed one year's leaves at the end of winter. 

 But neither of these defoliations has the slightest 

 reference to the ripening of the fruit ; and the time 

 of ripening of the fruit has no reference to any general 

 chemical causes, but to the particular constitution given 

 to the plant by an Almighty Creator. 



Liebig also makes plants play fast and loose in 

 reference to their carbonic acid and oxygen. In the 

 light, they absorb carbonic acid, and give off oxygen ; 

 vice versd^ in the dark. All plants throughout the 

 globe are, in point of time, for six months in the year 

 in the light, and for six months in the dark. There- 

 fore, all evergreen plants and pastures absorb and give 

 off each gas for equal periods of time ; not in equal 

 volumes, however, according to Liebig. 



' The proper, constant, and inexhaustible sources of 

 oxygen gas are the tropics and warm climates, where 

 a sky seldom clouded permits the glowing rays of the 

 sun to shine upon an immeasurably luxuriant vegeta- 

 tion. The temperate and cold zones, where artificial 

 warmth must replace deficient heat of the sun, produce, 

 on the contrary, carbonic acid in superabundance, 

 which is expended in the nutrition of the tropical 

 plants. The same stream of air which moves by the 

 revolution of the earth from the equator to the poles 

 brings to us, in its passage from the equator, the oxy- 

 gen generated there, and carries away the carbonic 

 acid formed during our winter.' 



