663 



grass 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 pre- 

 sence of fluorine. So far, however, as the plants named in the pre- 

 ceding table are concerned the author does not wish it to be inferred, 

 from the negative results which are detailed, that the plants in ques- 

 tion are totally devoid of fluorine. With larger quantities of their 

 ashes positive results would in all probability 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 Graminese and Equise- 

 taceae. 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 sufl5cient to etch glass deeply ; so that 

 the proportion of fluorine present, even in the plant-ashes which con- 

 tain 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 

 concordant 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 insolu- 

 ble fluosilicates (fluorides of silicon and of a metal) ; and a bamboo, for 

 example, secreting tabasheer, may effect this change where one less 

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

 stem may also affect the fixation of fluorides in the stems or trunks of 

 plants. 



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

 eminently two : (1) simple fluorides, such as that of calcium, which are 

 soluble in water, and through this medium are carried into the tissues 

 of plants; and (2) 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 apa- 

 tite and phosphorite, and in the animal kingdom in bones, shells, and 

 corals, as well as in blood, milk, and other fluids. 



A recent discovery of the author's, communicated to the Royal So- 

 ciety of Edinburgh, has shown that fluorides are much more widely 



