As a result of the broader view now taken with respect to the problems of soil fertility it is recognized that the conditions required for maximum growth must be sought from the facts of plant physiology as well as from those of soil science. For satisfactory growth a particular soil must satisfy certain conditions with respect to temperature, and to nutrient, water, and air supply to roots, the task of the investigator being to discover the best means of bringing the factors that govern these conditions under control. For this purpose the traditional chemical methods both of plant and of soil analyses have definite limitations ; some have been abandoned, others are still in use. In recent years interest has been renewed in the possibilities of the chemical analysis of the plant as a means of studying the nutrient relationships between the crop and the soil with respect to (1) the physiological requirement of a particular species and (2) the rate of supply of nutrients (10), i.e., the supplying power of the soil (27) . It is well established that the composition of a particular plant species is profoundly influenced by the composition of the soil (40). Consequently, in order to determine the influence of the soil on the action of fertilizers by means of analysis of the plant it is necessary to experiment first with plants growing in a relatively homogeneous soil {vide infra) using systematically laid out plots differentially fertilized. When this is done, the next step is to ascertain the nature of the variation in the composition of plants of the same species and variety in similarly treated (duplicate) plots, the soils of pairs of which may show all types of variations. There are many reasons, however, why the analysis of the entire plant is not the best means of approach toward the problem of control under field conditions. Apart altogether from the disadvantages of having to dig up and analyze whole plants, the results obtained by the gross analysis of a mass of heterogeneous organs possessing different functions are not a sufficiently sensitive comparative index in reflecting the responses of the plant to differences in its environment (soil and weather) (41). The classical investigations of Pierre (34) pointed to the sensitivity of the leaves to changes in composition resulting from differences in environment. But as long as no care was taken to differentiate between leaves of different ages little progress was made. The presentation of the gross analysis of leaves of all ages of a plant species, frequently seen even in present day literature,