154 THE ART OF CULTURE. 



all plants hitherto examined, and always in combi- 

 nation with alkalies or alkaline earths. Most seeds 

 contain certain quantities of phosphates. In the 

 seeds of different kinds of corn, particularly, there 

 is abundance of phosphate of magnesia. 



Plants obtain their phosphoric acid from the soil. 

 It is a constituent of all land capable of cultiva- 

 tion, and even the heath at Liineburg contains it 

 in appreciable quantity. Phosphoric acid has been 

 detected, also, in all mineral waters in which its 

 presence has been tested ; and in those in which 

 it has not been found, it has not been sought for. 

 The most superficial strata of the deposits of sul- 

 phuret of lead (galena) contain crystallized phos- 

 phate of lead (greenlead ore)-, clay-slate, which forms 

 extensive strata, is covered in many places with 

 crystals of phosphate of alumina ( Wavellite) ; all its 

 fractured surfaces are overlaid with it. Phosphate 

 of lime (Apatite) is found even in the volcanic bowl- 

 ders on the Laacher See in the Eifel, near Ander- 

 nach. 



The soil in which plants grow furnishes them 

 with phosphoric acid, and they in turn yield it to 

 animals, to be used in the formation of their bones, 

 and of those constituents of the brain which con- 

 tain phosphorus. Much more phosphorus is thus 

 afforded to the body than it requires, when flesh, 

 bread, fruit, and husks of grain are used for food, 

 and this excess in them is eliminated in the urine 

 and the solid excrements. We may form an idea 



