24 MISC. PUBLICATION 



influences. These factors are overlapping in their effect or work 

 simultaneously. One factor may influence another, as, for example, 

 the climate is a dominant influence in the development of the soil, 

 and through the soil, therefore, climate influences the plant. Differ- 

 ences in these factors will naturally operate to modify the plant in 

 different ways. For example, it is possible (1) for the mineral com- 

 position of two plants of the same variety growing in different soils 

 to be significantly different without there being any important 

 difference in their size or the distribution of their parts such as leaf, 

 stem, or seed head; (2) for the growth of the same variety of plants 

 to vary (differences in yield) in different soils without any important 

 differences in the proportions of the plant; (3) for two plants of the 

 same variety growing in different soils to have quite different dis- 

 tributions of leaf, stem, or head; and (4) for properties of soils to so 

 modify the quantities of plant constituents such as protein, carbo- 

 hydrates, lignin, and cellulose as to influence the percentage distribu- 

 tion of other constituents, such as a greater deposition of starch or 

 formation of lignin with a consequent reduction in the percentage 

 composition of the mineral elements. The properties of two soils 

 may be such as to modify the natural flora, and thus to produce 

 plants quite different in mineral composition. The evaluation of 

 these factors is still proceeding, and much valuable information of 

 fundamental importance is being obtained. 



For the purpose of this discussion, the subject of the variation in 

 the mineral content of plants and the factors that affect it will be 

 treated in three sections, namely: 



(1) The soil. The summarization of this literature will be as 

 complete as possible. 



(2) Fertilizers. Typical investigations, particularly as they relate 

 to our own soil types, and to the effect of the addition of one element 

 on the absorption of others, will be reviewed. 



(3) Miscellaneous. A few pertinent papers relating to the follow- 

 ing factors will be reviewed: Stage of maturity, climate, irrigation, 

 different varieties of the same species, and the composition of different 

 parts of the same plant. 



In discussing the effect of soils on plant composition, it must be 

 remembered that almost all work in this field should really be classified 

 as general environmental studies, since the effect of locality instead 

 of the soil as an isolated entity has more often been the subject of 

 inquiry. 



In 1873, Fliche and Grandeau (186) determined the principal 

 inorganic constituents in needles of the maritime pine (Pinus pinaster 

 Soland) grown in two soils in France. They found that the varia- 

 tions of phosphorus, magnesium, and sodium were small when com- 

 pared with those of calcium and potassium, which are given in table 8. 

 The data show that the calcium content of the needles of the tree 

 grown in the calcareous soil is higher than that of the other needles. 

 Although the effect of the calcareous soil at Bas-du-Cellier is reflected 

 in the calcium content of the plant growing on that soil, no explana- 

 tion is readily apparent as to the differences in potassium, except 

 that it is known that the availability of potassium in soils varies to 

 a far greater degree than does that of calcium. 



