662 



Table of Plants examined for Fluorine. The numbers represent grains of ashes, ex- 

 cept in the case of Tabasheer and Wood Opal. The blanks imply that the 

 weight was not known. 



Ash in Grains. 



Name of Plant. 



On this table the author remarked, that the sUiceous stems which 

 he had found to abound most in fluorine were exactly those which 

 contained most silica. In particular, deep etchings were procured 

 from the Equisetacege (horse-tails), and from the Gramineae (grasses), 

 especially the common bamboo. The last was known to contain 

 silica in such abundance that it collected within the joints in white 

 masses, nearly pure, and had long, under the name of tabasheer, been 

 an object of- interest to natural philosophers. The horse-tails were 

 scarcely less remarkable for the amount of silica contained in their stems, 

 which had led to the employment of one of them (Dutch rush, Equi- 

 setum hyemale) in polishing wood and metals. The African teak, 

 which, like the bamboo, is known sometimes to secrete silica, was 

 also found to contain fluorine, though much less largely than the 

 plants named ; whilst the strongly siliceous stems of barley and rye- 



