THE ASH OF PLANTS. 201 



two varieties from the field contained in their ash 11 to 

 13%. The proportion of ash was essentially the same in 

 both cases, viz., about 6%. Wolff's results with the oat 

 plant were entirely similar. 



Birner & Lucanus ( Vs. St., VIII, p. 141) found that 

 the supply of soluble silicates to the oat made its ash very 

 rich in silica (40%) but diminished the growth of straw, 

 without affecting that of the seed, as compared with 

 plants nearly destitute of silica. 



It is thus made certain that plants ordinarily rich in 

 silica may attain a high development in absence of this 

 substance. We shall see later, however (p. ), that 

 silica is probably not altogether useless to plants when 

 they grow under ordinary conditions. 



Jodin reports having bred maize by water-culture, with 

 the utmost practicable exclusion of silica, for four gener- 

 ations whereby this substance was reduced to the merest 

 traces without interference with the normal develop- 

 ment of the plant. (Ann. Agron., IX, p. 385.) 



The Ash-Ingredients, which are Indispensable 

 to Crops, may be taken up in Larger Quantity than 

 is Essential. More than eighty years ago, Saussure de- 

 scribed a simple experiment which is conclusive on this 

 point. He gathered a number of peppermint plants, and 

 in some determined the amount of dry matter, which 

 was 40.3 per cent. The roots of others were then im- 

 mersed in pure water, and the plants were allowed to veg- 

 etate 2 months in a place exposed to air and light, but 

 sheltered from rain. 



At the termination of the experiment, the plants, 

 which originally weighed 100, had increased to 216 parts, 

 and the dry matter of these plants, which at first was 

 40.3, had become 62 parts. The plants could have 

 acquired from the glass vessels and pure water no con- 

 siderable quantity of mineral matters. It is plain, then, 

 that the ash-ingredients which were contained in two 



