202 HOW CROPS GROW. 



parts of the peppermint were sufficient for the produc- 

 tion and existence of three parts. We may assume, 

 therefore, that at least one-third of the ash of the origi- 

 nal plants was in excess, and accidental. 



The fact of excessive absorption of essential ash-ingre- 

 dients is also demonstrated by the precise experiments of 

 Wolff on buckwheat, already described (see p. 164), 

 where the point in question is incidentally alluded to, 

 and the difficulties of deciding how much excess may 

 occur, are brought to notice. (See also pp. 192 arid 194 

 n regard to potassium and iron.) 



As further striking instances of the influence of the 

 nourishing medium on the quantity of ash-ingredients in 

 the plant, the following are adduced, which may serve to 

 put in still stronger light the fact that a plant does not 

 always require what it contains. 



Nobbe & Siegert have made a comparative study of 

 the composition of buckwheat, grown on the one hand in 

 garden soil, and on the other in an aqueous solution of 

 saline matters. (The solution contained magnesium 

 sulphate, calcium chloride, phosphate and nitrate of 

 potassium, with phosphate of iron, which together con- 

 stituted 0.316% of the liquid.) The ash-percentage was 

 much higher in the water-plants than in the garden- 

 plants, as shown by the subjoined figures. ( Vs. St., V, 

 p. 132.) 



Per cent of ash in 



Stems and leaves. Roots. Seeds. Entire plant. 



Water-plant 18.6 15.3 2.6 16.7 



Garden-plant 8.7 6.8 2.4 7.1 



We have seen that well-developed plants contain a 

 larger proportion of ash than feeble ones, when they 

 grow side by side in the same medium. In disregard of 

 this general rule, the water-plant in the present instance 

 has an ash-percentage double that of the land-plant, 

 although the former was a dwarf compared with the lat- 

 ter, yielding but as much dry matter. The seeds, how- 

 ever, are scarcely different in composition. 



