24 DIFFERENCES IN THE ASH OF PLANTS. 



tween various plants, but between the parts of the 

 same plant. 



If we examine the straw of wheat, we find usually 

 6 or 7 per cent of ash; the leaf contains 7 or 8 per cent, 

 and the grain not more than 1 or 2 per cent. So in 

 turnips or beets, the dried roots have no more than 

 from 1 to 2 per cent of ash, while the dried leaves 

 often leave from 20 to 30. These facts are to be 

 remembered. 



When we pursue t)ur researches a step further, and 

 separate the substances which make up the ash of dif- 

 ferent plants, we find that here also is a great variation. 

 The ash of potatoes is more than half potash, while the 

 ash in the grain of wheat contains much less potash, 

 but is about half phosphoric acid. The ash of clover 

 and lucerne often contains twice as much lime as that 

 of herdsgrass or timothy hay. 



We may thus divide plants into classes according 

 to the composition of their ash. In the ash from the 

 seed of wheat and all of our cultivated grains, phos- 

 phoric acid is the leading ingredient; in that from 

 turnips, beets and other roots, it is much less, while the 

 alkalies potash and soda increase; in the tubers of the 

 potato they constitute more than half; in the grasses, 

 lime and silica are more abundant, and in some, as 

 the clovers, lime becomes a leading substance; in the 

 stems of most trees lime abounds yet more, and in many 

 cases exceeds in quantity any thing else. These facts 

 have a marked bearing on many practical points which 

 we have yet to consider. 



It was stated that the quantity of ash varied in 

 different parts of the same plant, as, for example, in 

 the straw and the grain of wheat. This variation in 

 quantity is not more marked than that in the com- 

 position of these two ashes. In the ash of the straw 

 we find that there is a great proportion of silica, and 

 very little phosphoric acid; while in that of the grain, 



