ABSORPTION OF WATER. 



Finally, the absorbent capacity of the plant varies at 

 different periods of its life. We learn from von Gorup- 

 Besanez's analyses of Trapa given above, that that plant 

 contains a larger proportion of ash at an early than at a 

 later period of its vegetation, a result which has been ob- 

 tained also in the case of other plants. We may cite Arendt's 

 observations on the Oat-plant in illustration. 



Arendt analysed Oat-plants at different times during their growth; 

 taking the quantity of silica absorbed as a standard of comparison and 

 fixing it at 10, he found the other constituents had been absorbed in the 

 following proportions : 



But the amount of a substance absorbed is not determined 

 solely by the specific absorbent capacity of the plant, for we 

 found in discussing de Saussure's law that the larger the 

 proportion of any given substance in the solution supplied 

 to the roots, the larger was the amount absorbed. The com- 

 position of the soil or of the solution in which the roots of 

 a plant are growing must have an important effect upon the 

 composition of the ash. This has been abundantly proved 

 by a large number of analyses, of which we may cite the 

 following. 



Herapath analysed light Oats grown upon sandy soil, and heavy Oats 

 grown on the same soil after manuring with river-mud (warping). 



Light Oats Heavy Oats 



Potash 9-8 13-1 per cent. 



Soda 4-6 7-2 



Lime 6'8 4-2 



Phosphorus pentoxide 97 17*6 



Silica 56-5 45-6 



