80 CLASSniCATloN OF PLANTS, 



about one-third. In the straw ash there is but 3 per 

 cent of phosphoric acid, and only 10 per cent of pot- 

 ash; magnesia is also much less. 



6. In the grain there is not quite 1| per cent of 

 silica, but in the straw there is nearly 70 per cent. 

 Silica, then, is the leading ingredient in the ash of the 

 straw, phosphoric acid in that of the grain. It is 

 silica which gives the straw its stiffness, strength, and 

 elasticity; when there is not a sufficient supply of it, 

 the straw can not uphold the weight of the grain, and 

 falls down or lodges, as the farmers say. 



c. The reason why nearly all of the phosphoric 

 acid is found in the grain, will be apparent as we 

 proceed to another part of this treatise. This acid is 

 shown by the table to be more abundant than anything 

 else in the ash of rye and oats: the same thing is true 

 of barley and buckwheat. In the straw of all these, 

 there is also a preponderance of silica. In the grain 

 of Indian corn, phosphoric acid is very abundant, but 

 there is not so much silica in the stalk as in the straw 

 of grain. 



The ash from all of these grains differs from the 

 ash of potatoes and turnips in one essential particular: 

 in the two last, phosphoric acid is comparatively a 

 small quantity, being only about one-tenth; here, on 

 the contrary, we find that potash is the most abundant 

 substance of all, particularly in potatoes, where it is a 

 little more than half of the whole. In the ash of both 

 potato and turnip tops, lime also abounds, and often 

 phosphoric acid. Potash and soda too are here among 

 the most prominent ingredients. 



If now we look at the ash of meadow hay, we 

 perceive that there is still another difference : potash 

 a nil soda together are about 20 per cent, phosphoric 

 acid is but 6 per cent, while lime is more abundant 

 than anything else with the exception of silica, which 

 last is required to give strength to the stalk as in the 

 straw. 



