ODOUR OF PLANTS. 77 



flinty earth in the form of a most exquisite 

 powder, and this accounts for the utility of 

 burnt straw in giving the last polish to mar- 

 ble. How great is the contrast between this 

 production, if it be a secretion, of the tender 

 vegetable frame, and those exhalations which 

 constitute the perfume of flowers ! One is 

 among the most permanent substances in 

 Nature, an ingredient in the primeval moun- 

 tains of the globe ; the other the invisible un- 

 tan° ible breath of a moment ! 



The odour of plants is unquestionably of a 

 resinous nature, a volatile essential oil, and 

 several phenomena attending it well deserve 

 our attentive consideration. Its general na- 

 ture is evinced by its ready union with spirits 

 or oil, not with water ; yet the moisture of 

 the atmosphere seems, in many instances, 

 powerfully to favour its diffusion. This I ap- 

 prehend to arise more from the favourable ac- 

 tion of such moisture upon the health and vi- 

 gour of the plant itself, thus occasionally pro- 

 moting its odorous secretions, than from the 

 fitness of the atmosphere, so circumstanced, 

 to convey them. Both causes however may 

 operate, ^i number of flowers which have no 



