Several investigators (1, 2, 5, 10, 11, 13) have made use of plant analysis as an aid in diagnosing the nutrient requirement of plants and as a possible means of determining plant nutrient deficiencies in the soil. It has been shown as the of nutrients not in ample supply is increased, other factors being constant, plant growth is promoted and internal concentration of nutrient in the plant rises, at least in certain plant organs and at certain stages of development. Macy (6) has distinguished three portions of a curve relating yield to internal nutrient concentration. The section of the curve denoting minimum percentage'* shows a small increase in yield with constant internal concentration; the section of adjustment'' shows an increase in yield and internal concentration; and finally the section of consumption' * shows the yield remains constant with increasing internal concentration. Macy defines the transition between poverty adjustment and luxury consumption as the percentage. Ulrich (13) defines the critical nutrient of a plant as that narrow range of nutrient concentration in which the growth rate or yield of the plant first begins to decrease in comparison to plants at a higher nutrient This is determined by growing plants in media supplying two different amounts of the limiting nutrient, while other growth factors are held constant. At first there is no apparent difference in growth, but later the growth of the plants in the medium with the smaller amount of the nutrient under study is less than the growth of the plants in the medium with the larger amount of nutrient. The concentration of the nutrient under study in a suitable part of the plant harvested at this point of decreasing growth is a critical concentration or nutrient level. Although the nutrient level at this point varies for different species, it tends to be relatively constant for specific organs of the same plant, provided seasonal factors of light and temperature, and concentration of other ions in the nutrient medium do not inhibit normal plant growth. The red raspberry, Rubus idaeus L., is one of the important brambles grown in the state of Washington. Although the exact fertilizer requirements for this crop are not known, the use of mixed fertilizers is a general practice considered necessary for the production of high yields. The ? Published as Scientific Paper No. 861, Agricultural Experiment Stations, Institute of Agricultural Sciences, State College of Washington, Pullman, Washington. 617