POWER OF VEGETATION IN PLANTS. 83 



chiefly delight to vegetate are particularly exposed 

 to the influence of the sun. In that hot dry summer 

 of 1825, when vegetation was in general burnt up 

 and withered away, yet did the snapdragon continue 

 to exist on parched walls, and draw nutriment from 

 sources apparently unable to afford it ; not in full 

 vigour certainly, but in a state of verdure beyond 

 any of its associates. The common burnet (pote- 

 rium sanyuisorba) of our pastures, in a remarkable 

 degree, likewise possesses this faculty of preserving 

 its verdure, and flourishing amid surrounding ari- 

 dity and exhaustion. It is probable that these 

 plants, and some others, have the power of imbib- 

 ing that insensible moisture, which arises from the 

 earth even in the driest weather, or from the air 

 which passes over them. The immense evaporation 

 proceeding from the earth, even in the hottest sea- 

 son, supplies the air constantly with moisture; and 

 as every square foot of this element can sustain 

 eleven grains of water, an abundant provision is 

 made for every demand. We can do little more 

 than note these facts : to attempt to reason upon the 

 causes, why particular plants are endowed with pe- 

 culiar faculties, would be mere idleness; yet, in re- 

 marking this, we cannot pass over the conviction, 

 that the continual escape of moisture from one body, 

 and its imbibition by another, this unremitting mo- 

 tion and circulation of matter, are parts of that 

 wonderful ordination, whereby the beneficence and 

 wisdom of Providence are manifested : without the 

 agency of evaporation, not dwelling on the infini- 



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