METHODS OF INVESTIGATING MICRO-NUTRIENT PROBLEMS

Abstract

THE PURIFICATION OF MATERIALS USED IN CULTURE EXPERIMENTS THE existence of the micro-nutrients raises a number of problems which can only be solved after the development of methods designed specially to deal with them. In the first place the question inevitably arises as to how we can be certain that any particular element is really essential or not. This is obviously a problem of mineral nutrition requiring immediate solution; it is clearly an essential preliminary for all investigations on the micro-nutrients that we should know what these are. It has already been pointed out that the essentiality of the micro-nutrients for plant development was overlooked for half a century simply because an adequate supply of them was introduced into the culture (1) from the seed from which the plant developed, (2) from impurities present in the water and salts used in preparing the culture solutions, and (3) by solution from the vessels used to hold the culture solutions. Hence the problem of determining the micro-nutrients clearly resolves itself into devising means for preventing the introduction of micro-nutrients from these three sources. If this can be done the effect of the absence or presence of any particular element in the culture medium can then be determined for a wide range of plant species. The prevention of the introduction of any particular elements from the seed used for the cultures is perhaps scarcely possible. But when the seed is small the amount of any micro-nutrient present in it is likely to be negligible, and when the seed is large the amount introduced can often be considerably reduced by removal of the cotyledons from the seedling as soon as the latter is established. Reference has already been made to Lipman's method of meeting the difficulty in his experiments with buck-wheat, in which seed was used from plants-grown in culture solutions devoid of chlorine. It appears clear that by this procedure seed was obtained containing a negligibly small quantity of this element. The problem of obtaining water and salts free from the trace elements for work on the nutrition of fungi has been dealt with by a number of workers, notably Steinberg (1919,1935b).