Several years ago the writer's attention was called to the apparently favourable influence of field peas on oats when the two were grown together. The rank growth of the oats, their dark-green colour and the delayed ripening gave every indication of an abundant supply of available nitrogen compounds. On the other hand, oats seeded without the peas, at about the same time, were less rank in their growth and matured at an earlier date. Further observation and inquiry strengthened the impression in the writer's mind that the associative growth of legumes and non-legumes is frequently advantageous to the latter in that they are supplied with nitrogen compounds derived either from the decay of the fibrous roots of the legumes, or from the soluble materials passing out of the roots into the surrounding soil.