THE ASH OF PLAKTS. 159 



much more considerable. Wheat-straw ranges from 3.8 

 to 6.9 ; pea-straw, from 6.5 to 9.4 per cent. In fleshy 

 roots, the Tariations are great ; thus turnips range from 

 6 to 21 per cent. The extremest variations in ash-con- 

 tent are, however, found, in general, in the succulent 

 foliage. Turnip tops range from 10.7 to 19.7; potato 

 tops vary from 11 to near 20, and tobacco from 19 to 37 

 per cent. 



Wolff {Die Naturgesetzlichen Orundlagen des Acker- 

 baus, 3 Aufl., p. 117) has deduced from a large number 

 of analyses the following averages for three important 

 classes of agricultural plants, viz. : 



drain. Straw. 



Cereal crops 2 per cent. 6.35 per cent. 



Leguminous crops 3 " " 5 " " 



OU-plants 4 " " 4.^ " " 



More general averages are as follows (Wolff, loe. cit.) : 



Annual and biennial plants. 



Seeds 3 per cent. 



Stems 5 *' " 



Roots 4 " " 



Leaves IB " " 



Perennial plants. 



Seeds 3 per cent. 



Wood 1 " " 



Bark 7 " " 



Leaves 10 " " 



We may conclude this section by stating three propo- 

 sitions which are proved in part by the "facts that have 

 been already presented, and which are a summing up of 

 the most important points in our knowledge of this sub- 

 ject. 



1. Ash-ingredients are indispensable to the life and 

 growth of all plants. In mold, yeast, and other plants 

 of the simplest kind, as well as in those of the higher or- 

 ders, analysis never fails to recognize a proportion of 

 fixed matters. We must hence conclude that these are 

 necessary to the primary acts of vegetation, that atmos- 

 pheric food cannot be assimilated, that vegetable matter 

 cannot be organized, except with the cooperation of those 

 substances which are invariably found in the ashes of the 

 plant". This proposition is demonstrated in the most 

 conclusive manner by numerous synthetic experiments. 



