41 



in the ash composition of plants which are at different stages of 

 maturity or grown imder iinhke chinatic conditions are vahieless as 

 showing the effect of the cliaracter of the soil. 



But even under hke conditions of chmate, water supply, character 

 of the soil, etc., the ash composition of plants can be varied m some 

 directions without affecting the growth appreciably. This involves 

 the question of "luxus consumption." From studies that have been 

 made of the utihzation of nitrogen, phosphoric acid, and potash by 

 the plant, it is apparent that when there is an excess of these nutrients 

 present a plant may take up more of these elements than are neces- 

 sary for growth.^ If, however, a certain greater amount of these 

 elements is absorbed, the growth is depressed. Hence we may 

 conclude that there is a minimum amount of an element required 

 for a plant to make a maximum growth; that the plant can absorb 

 luxus above this necessary amount without injury, but when the 

 excess absorption exceeds a certain point injury to growth results. 



On this basis some changes in ash are significant while other's are 

 not. The greater the change in any particular plant, however, the 

 greater the probabihty that it is of consequence. The same order 

 of change is probably not equally productive of effect on all plants, 

 however, as some plants seem more sensitive to changes in their ash 

 content than others. Nor is the same order of change necessarily 

 significant for all the mineral elements.^ 



The question whether there ai-e certain ratios that shoidd exist 

 between the elements in the ash, also has a bearing on what changes 

 in the ash are significant. Wliile it is well proven that sodium can 

 partially substitute potassium in the plant, it has not been established 

 that there should be a definite ratio between these two bases.^ Ac- 

 cording to some investigators, Ume and magnesia can substitute each 

 other to a certain extent in the plant,* while others are more of the 

 opinion that these elements should be present in a definite ratio. 

 According to Champion and Pellet, the bases are more or less capable 

 of mutual substitution but the sum of their chemical equivalents 

 should be constant, each species of plant having a different constant." 



In short, it is reasonably sure that the differences in ash composi- 

 tion of the plants grown on the calcareous soils were induced by the 

 carbonate of hme and not by some climatic or accidental factor. But 

 it is not certain that these differences in ash composition affected the 

 growth, since we have no general knowledge as to what changes in 

 ash composition are indicative of impaired nutrition. The most 



■ Jordan, W. H., New York State .Sta. Bui. 360, p. 76. 



* In the experiments of Dikow, Wilms, and Atterberg (loc. cit.), the P^O^ content of the plants showed 

 less variation than the N and KjO content. 



3 Hartwell, B. L., and Pember, F. R., Rhode Island Sta. Rpt. 1908, p. 24;i. 



< Malaguli and Durocher, Ann. Sci. Nat. Bot., 4. ser., 9 (1858), p. 222. 



s Champion, P., and Pellet, H., Compt. Rend. Acad. Soi. [Paris], 80 (1875), p. 1588; Biedennanns Centbl . 

 Agr. Chem., 8 (1875), p. 242; 9 (1876). p. 118. 



