ABSORPTION OF MINERAL ELEMENTS BY PLANTS 267 



tative period of oats into five sections, the author observed in 

 the first period 39 per cent of the total amount; in the second, 

 31 per cent; in the third, 21 per cent; in the fourth, 9 per cent; 

 and in the fifth, 0. For calcium, the corresponding figures were 

 30, 28, 21, 20, and 1 per cent; for magnesium, 24, 18, 16, 26, and 

 16 per cent. Like magnesium, phosphoric acid and nitrogen are 

 absorbed fairly uniformly throughout the vegetative period of oats. 



The time of absorption of different elements varies rather 

 mdely for plants of different types. Thus, for instance, the 

 curve of the absorption of ash elements for oats, being very high 

 initially, falls rapidly; for peas, on the contrary, it rises con- 

 tinuously to the end of vegetative growth. Probably this is 

 connected with the fact that oats complete their growth soon after 

 heading; while in peas, flow^ering is prolonged, and the plant has 

 a more or less continuous type of development. 



Toward the end of the vegetative period of annuals, when 

 synthetic activity has ceased and only processes of translocation 

 of accumulated substances into the seeds take place, considerable 

 losses of ash elements may frequently be observed. According 

 to Andre and other authors, the loss of potassium may reach 

 at the end of the vegetative period up to }^ of the maximum 

 amount accumulated; the loss of calcium, up to f^i; and that of 

 magnesium, up to Ho- It is probable that a part of these losses 

 may be attributed to the washing out of salts from dead leaves 

 by rain, but certainly a considerable loss is chargeable to the 

 backward translocation of substances into the root system. It 

 is interesting to note that the greatest translocation is observed 

 with potassium, which is present in the plant almost entirely in 

 the ionic state, since it does not form any complex compound 

 with organic substances. Most plants are capable of gro\^dng 

 on different soils, for almost all contain sufficient nutrient sub- 

 stances for their development. Hence, climate permitting, it is 

 possible to raise the same crop plants in widely differing soil 

 zones. Still, not all soils can satisfy the requirements of different 

 plants to the same degree, and the distribution of the wild flora 

 can often serve as an excellent indicator of soil properties. A 

 few characteristic plants may be considered as definite indicators 

 of certain soil conditions, not only of its chemical composi- 

 tion but its physical character and water-holding capacity as 

 well. 



