ESSENTIALS OF PLANT LIFE IQ 



When the plant contained less than 0.33 per cent, of phosphoric 

 acid, it was not well developed. When the percentage of phos- 

 phoric acid was increased over 0.33 per cent., the quantity of 

 straw was little affected, but the quantity of grain increased. In 

 the presence of silica, equally as much grain could be produced 

 with 0.33 per cent, phosphoric acid. Wolff therefore concludes 

 that the minimum quantity of phosphoric acid required by the 

 entire oat plant is 0.33 per cent, of the dry material. 



Similar series of experiments were made with potash, lime, 

 and other forms of plant food. From these experiments Wolff 1 

 concludes that the minimum requirements of the oat plant, based 

 on the dry matter of the entire plant, is as follows : 



Per cent. 



Phosphoric acid 0.35 



Potash 0.8 



Lime o. 2 



Magnesia 0.2 



Sulphuric acid 0.2 



Total of the essential constituents 1.75 



Pure ash necessary 3.00 



Nitrogen i.oo 



While the oat plant can get along with 1.75 per cent, of the 

 essential ash constituents, a total of 3.00 per cent, of pure ash 

 is absolutely necessary. It was impossible to grow a plant with 

 less than 3.00 per cent, of ash. The additional 1.25 per cent, 

 may consist either of essential elements, or of unessential ele- 

 ments, such as silica or soda, but the quantity required must be 

 made up in some way or other. We may term the ash in excess 

 of the sum of the essential ash ingredients, the indifferent ash. 

 The unessential elements can be useful to the plant in making 

 up its indifferent ash, which is, however, essential. Various sub- 

 stances sometimes added to the soil, such as salt, gypsum, lime, 

 etc., may be useful in satisfying the need of the plant for indiffer- 

 ent ash. Since 1.25 per cent, of the necessary 3.00 per cent, of 

 the ash of oats may be of varying nature, and since plants may 

 take up ash in excess of their needs, the ash of the plant is 

 subject to considerable variation in composition. 

 1 Jahresber. Agr. Chem., 1875, p. 251. 



