There was a considerable development of roots in the upper part of pot 1, and a number of root-tubercles were formed, owing to the fact, as proved by subsequent experiments, that the sand was not sterilized before planting the peas. The roots in pots 2 and 3, inoculated with soil-extract, were more abundant than in pot 1, and the root-tubercles were decidedly more numerous and frequently in clusters. The above-ground growth was more luxuriant in pots 2 and 3 than in pot 1, and "in the total vegetable matter there was in pot 2 more than twice, and in pot 3 nearly twice as much, nitrogen as in pot 1 without soil-extract."
A comparison of the total nitrogen in the soil and plants at the close of the experiment with the original nitrogen in the soil and seeds showed that "in pot 1, with the impure and not sterilized sand, but without soil-extract, there was more than three times as much nitrogen in the products as in the soil and seed; in pot 2, with soil-extract, there was about five times as much; and in pot 3, also with soil-extract, there was more than four times as much." There was very little difference in the amount of nitrogen in the soils at the beginning and the close of the experiments, and, neglecting this, it appears that "the nitrogen in the substance grown was, in pot 1, nine and one half-fold; in pot 2, nearly eighteenfold; and in pot 3, nearly fifteen-fold that supplied in the seed."
In 1889 similar experiments were made with peas, red clover, vetches, blue lupines, yellow lupines, and lucern. For the lupines and lucern glazed earthenware pots, six inches in diameter and fifteen inches deep, were provided, and for the other plants the same pots were used as in 1888.
"The sand used was a rather coarse white quartz sand, from which the coarser and the finer portions were removed by sifting, and more of the finer by washing and decantation, first in well, and afterward in distilled water.
"In each case the sand was mixed with 0·1 per cent of the plant-ash, and 0·1 per cent of calcium carbonate." The prepared sand was sterilized by keeping it for several days at a temperature of nearly 100° C. in a water-bath.
"There were four pots of each description of plant." Of the peas, clover, vetches, and lucern there was one pot of each of the prepared quartz sand without inoculation with soil-extract; two pots of the prepared quartz sand inoculated with the microbes of a garden-soil extract; and one pot of garden soil itself. Of the blue and the yellow lupines there was one pot of each of the prepared, but not inoculated, quartz sand; two pots of the prepared quartz sand inoculated with an extract of a soil from a field where lupines were growing; and one pot of the lupine soil itself, to which was added 0*01 per cent of lupine plant-ash.
"The soil-extracts were in all cases added on July 9th, before
