[ 4 ] 



have been treated with the greater! 

 attention, and have thrown much 

 light upon this fubjedt. 



This celebrated author has taken 

 a great deal of notice of thofe air 

 bubbles which cover the leaves 

 when plunged under water. He 

 fays, p. 26, that the leaves draw 

 thefe bubbles from the water. He 

 is the more perfuaded that this is 

 the cafe, becaufe he found thefe 

 bubbles did not appear when the 

 water had been boiled fome time, 

 and appeared more when the wa- 

 ter is impregnated with air, by blow- 

 ing in it. He had alfo obferved, 

 that they did not appear after fun- 

 fet. Page 31, he explains his opi- 

 nion farther upon this head: he 

 fays, that thefe air bubbles are pro- 

 duced by common air adhering to 

 the external furface of the leaves, 

 3 which 



