402 



ABSORPTION OF MINERAL SALTS 



minum, manganese, sodium, boron, caesium, lithium, fluorine, rubidium, 

 barium, strontium, bromine, mercury, zinc, tin, lead, thallium, titanium, 

 arsenic, selenium, iodine, chromium, cobalt, vanadium, copper, and silver. 



Of this somev^^hat extensive list only the first fifteen of these elements are 

 found regularly in plants in appreciable quantities and several of these are 

 apparently not essential. On the other hand certain other elements which 

 are seldom present in more than minute traces are indispensable, at least for 

 the continued growth of some species. 



The elemental composition of a mature corn (maize) plant is illustrated 

 by the data in Table 38, which may be taken as fairly representative for 

 plants in general. 



TABLE 38— ELEMENTAL ANALYSIS OF THE STEM, LEAVES, COB, AND GRAIN OF A MATURE CORN 

 PLANT ("pride of SALINe"), BASED ON AVERAGE VALUES FOR FIVE PLANTS (dATA OF 

 LATSHAW AND MILLER, 1 924) 



The composition of plant ash varies both with the species and the en- 

 vironmental conditions under which the plant has developed. Comparative 

 figures on the percentages of five of the more important mineral elements in 

 several different species of plants growing in the same soil are given in 

 Table 39. 



As the data in this table show, even when growing under identical soil 

 and climatic conditions, different species of plants contain very different 

 proportions of the various elements obtained from the soil. Until the mech- 

 anism of the absorption and translocation of mineral elements by plants is 



