230 Botanical Society of Edinburgh. 



from the Equisetacese and from the Graminese, 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 (^Equisetum 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 Ryegrass also yielded the element in 

 marked quantity. The Sugar-cane, however, gave less striking results 

 than might have been expected, and the same remark applied to the 

 Malacca- cane. Two specimens of silicified wood and one of Tabasheer 

 gave no evidence of the presence of fluorine. So far, however, as the 

 plants named in the preceding table are concerned, the author does 

 not wish it to be inferred from the negative results which are detailed, 

 that the plants in question are totally devoid of fluorine. With 

 larger quantities of their ashes, positive results would, in all proba- 

 bility, be obtained. 



The author's general conclusions were as follows : — 1st, that fluo- 

 rine occurs in a large number of plants ; 2nd, that it occurs in marked 

 quantity in the siliceous stems of the Gramineae and Equisetacese ; 

 3rd, that the quantity present is in all cases very small ; for although 

 exact quantitative results were not obtained, it is well known that a 

 fraction of a grain of fluoride will yield with oil of vitriol a quantity 

 of hydrofluoric acid suflicient to etch glass deeply, so that the pro- 

 portion of fluorine present, even in the plant-ashes which contain it 

 most abundantly, does not probably amount to more than a fraction 

 per cent, of their weight. The proportion of fluorine appears to be 

 variable, for different specimens of the same plant did not yield con- 

 cordant results. 



In this, however, there is nothing anomalous, for some Bamboos 

 yield Tabasheer largely, whilst others are found to contain none. It 

 seems not unlikely that soluble fluorides ascending the siliceous stem 

 of a plant, on their way to the seeds or fruits in which they finally 

 accumulate, may be arrested by the silica, and converted into inso- 

 luble fluosilicates (fluorides of silicon and of a metal) ; and a Bamboo, 

 for example, secreting Tabasheer, may eff^ect this change where one 

 less rich in silica cannot determine it. The slow or quick drying of 

 a stem may also afi*ect the fixation of fluorides in the stems or trunks 

 of plants. 



The sources of the fluorine found in plants may be regarded as 

 preeminently two, — 1st, simple fluorides, such as that of calcium, 

 which are soluble in water, and through this medium are carried into 

 the tissues of plants ; and 2nd, compounds of fluorides with other 

 salts, of which the most important is probably the combination of 

 phosphate of lime with fluoride of calcium. This occurs in the 

 mineral kingdom in apatite and phosphorite, and in the animal king- 

 dom in bones, shells and corals, as well as in blood, milk, and other 

 fluids. 



