74 FLINTY SECRETION. 



ject in the Phil. Trans, for 1790 and 1791. It is even 

 found occasionally in the Bamboo cultivated in our hot- 

 houses. But we need not search exotic plants for flinty 

 earth. I have already, in speaking of the Cuticle, chap- 

 ter 3d, alluded to the discoveries of Mr. Davy, Professor 

 of Chemistry at the Royal Institution, on this subject. 

 That able chemist has detected pure flint in the cuticle 

 of various plants of the family of Grasses, in the Cane 

 (a kind of Palm) and in the Rough Horsetail, Eqmsetum 

 hyemale^ Engl. Bot. t. 915. (10) In the latter it is very 

 copious, and so disposed as to make a natural file, which 

 renders this plant useful in various manufactures, for 

 even brass cannot resist its action. Common Wheat 

 straw, when burnt, is found to contain a portion of 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 marble. Ho^v great is the contrast between 

 this production, if it be a secretion, of the tender vege- 

 table frame, and those exhalations which constitute the 

 perfume of flowers ! Oiie is among the most permanent 

 substaaccs in Nature, an ingredient in the primaeval 

 mountains of the globe ; the other the invisible untan. 

 gible breath of a moment ! 



The odour of plants is unquestionably of a resinous 

 nature, a volatile essential oil and several phaanomena 

 attending it well deserve our attentive consideration. 

 Its general nature is evinced by its ready union with 

 spirits or oil, not with water ; yet the moisture of the 

 atmosphere seems, in many instances, poweifully to fa- 



(10) [Used in this country under the name of Scouring Rush.] 



