98 THE WORLD'S LUMBER ROOM. 



the minerals are already in the soil ; and if they are absent 

 the farmer himself must supply them in the shape of bones, 

 ashes, &c. 



Many grasses, especially the stiff harsh kinds, and all 

 varieties of corn, contain much silica or flint. What they 

 want it for is not clear, for it does not seem needed to give 

 strength to their stems, as has been supposed ; but they 

 cannot do without it. In barley straw more than half the 

 ash is flint, in winter wheat 41 per cent, in meadow hay 29 

 per cent* 



Among trees, while the willow and oak contain very 

 little flint, but a great deal of lime, the Scotch fir takes as 

 much lime as the willow, and twenty-one times as much flint ; 

 and the Cauto tree of South America has bark as hard as 

 soft sandstone from the quantity of flint it contains, and the 

 natives of Trinidad use its ashes in place of sand, with the 

 clay of which they make their pottery. The smooth glossy 

 rind of the bamboo, which contains 70 per cent, of flint, 

 will strike fire with steel, and the same substance collects in 

 hard lumps like opal in the joints of the stem. 



There is flint again in the hairs of the nettle, in hemp, 

 and in hops, and all the best vegetable weaving fabrics, 

 except cotton, contain a great deal. Of all our native plants, 

 however, none contain more than the horse-tails, formerly 



* The proportion of ash of all sorts, though not invariable, is about as 

 follows : 



Per cent. 



Field beet i8'a 



Red clover 67 



Wheat straw 5*4 



Wheat grain 2*0 



Per cent. 



Pea straw 7 '9 



Pea grain 27 



Fir bark 2-0 



Fir wood . 0-3 



