ESSENTIALS OF PLANT LIFE 



in potash from 6.8 : 22.00 or over I : 3. Inspection of the table 

 shows that phosphoric acid varies in a similar manner, though 

 the variations are not so large. In these experiments, at least, 

 the effect of the season is greater than the effect of fertilizers or 

 the soil. 



Ash of Strong and Weak Plants. Various chemists have select- 

 ed strong plants and weak plants growing in the same field at the 

 same time, and subjected them to analysis. Some analyses of 

 this kind are given in the following table 1 : 



COMPOSITION OF STRONG AND WEAK PLANTS. 



The weak plants contain a smaller percentage of ash than the 

 strong plants. The percentages of potash and lime are smaller, 

 and the percentages of silica are much larger in the ash of the 

 weak plants. 



Effect of Stage of Growth on Ash. The percentage of ash 

 shows the relation between the organic matter formed and min- 

 eral matter taken up by the plant. The absorption of mineral 

 matter from the soil, and the production of organic matter by the 

 plant, do not proceed at the same rate, consequently the per- 

 centage of ash in the plant varies at different periods of time. 

 Changes in the ash content of plants at different periods of 

 growth depend upon the kind of plant, and the part of the plant 

 under consideration. As a general rule, we find that the ash con- 

 tent is greatest in the young plant, and that it decreases with the 

 1 Wolff's Ashen Analysen. 

 3 



