SECT. V. EARTHS. 75 



reduced to ashes. But the same principles were 

 found in them all ; amongst which was a portion of 

 silica ; -whence Lampadius concluded that the silica 

 found in plants is merely the result of vegetation, 

 having no relation whatever to the soil in which the 

 plants grow. 



But this conclusion was by much too hasty, and 

 has been since shown to be most palpably erroneous ; 

 because Lampadius does not take into the calcula- 

 tion the constituent principles of the cow-dung 

 with which his earths were mixed, the very sub- 

 stance from which his plants must have derived the 

 greater part of their nourishment. If this precau- 

 tion had been taken, his conclusion must have been 

 very different : for it has been ascertained by Ruc- 

 kert that dung does actually contain a portion of 

 silica ;* which in the case of cow-dung will appear 

 the less surprising if it is only recollected that the 

 plants which cows principally feed on do themselves 

 contain a portion of silica. To the cow-dung, 

 therefore, with which the different earths were 

 manured, the origin of silica may be traced. It was 

 thus of necessity found in them all, though not 

 perhaps in an equal proportion. 



Saussnre, in adverting to the experiment ofTheopi- 

 Lampadius, exposes indeed the absurdity of his ab ~ 

 conclusion ; but deduces from it another which is 

 perhaps equally exceptionable namely, that plants 

 growing in calcareous and granitic sand, mixed with 

 * Sur. la Vcgct. chap. ix. sect. iij. 



