[ 183 



LECTURE V. 



On the nature and Constiution of the Atmosphere; and 

 its Influence on Vegetables. Of the Germination of 

 Seeds. Of the Functions of Plants in their differ- 

 ent Stages of Growth; with a general view of the 

 Progress ofVegetation. 



The constitution of the atmosphere has been al- 

 ready generally referred to in the preceding Lectures. 

 Water, carbonic acid gas, oxygene, and azote, have 

 been mentioned as the principal substances compo- 

 sing it; but more minute enquiries respecting their na- 

 ture and agencies are necessary to afford correct 

 views of the uses of the atmosphere in vegetation. 



On these enquiries I now propose to enter; the 

 pursuit of them, I hope, will offer some objects of 

 practical use in farming; and present some philosophi- 

 cal illustrations of the manner in which plants are 

 nourished; their organs unfolded, and their functions 

 developed. 



If some of the salt called muriate of lime that 

 has been just heated red be exposed to the air, even 

 in the driest and coldest wheather, it will increase in 

 weight and become moist; and in a certain time will be 

 converted into a fluid. If put into a retort and heated, 

 it will yield pure water; will gradually recover its 

 pristine state; and, if heated red, its former weight: so 

 that it is evident, that the water united to it was derived 



