SECT. XXVII. EARTHS. 47 1 



contain no carbonate of lime ; but tbey abound in 

 phosphate of potass. Hence the ashes of plants, at 

 the period of the maturity of the fruit, yield less 

 carbonate of lime than at any previous period.* 



2dly, Silica. Silica is not found to exist in a 

 great proportion in the ashes of vegetables, unless 

 they have been previously deprived of their salts 

 and phosphates by washing ; but when the plants 

 are washed in water the proportion of their silica 

 augments. The ashes of the leaves of the Hazel 

 gathered in May yielded 2' 5 parts of silica in 

 100. The same leaves washed yielded four parts in 

 100. 



Young plants and leaves bursting from the bud 

 contain but little of silica in their ashes ; but the 

 proportion of silica augments as the parts are de- 

 veloped. But perhaps this is owing to the diminu- 

 tion of the alkaline salts. The ashes of some stalks 

 of Wheat gathered a month before the time of 

 flowering, and having some of the radical leaves 

 withered, contained -^- of silica and T 6 T V of alkaline 

 salts. At the period of their flowering, and when 

 more of their leaves were withered, the ashes con- 

 tained 32 parts of silica and 54 of alkaline salts. 



Seeds divested of their external covering contain 

 less silica than the stem furnished with its leaves ; 

 and it is somewhat remarkable that there are trees 

 of which the bark, alburnum, and wood, contain 

 scarcely any silica, and the leaves a great deal, par- 

 * Saussure sur la Vegetation, chap. ix. sect. vi. 



