Page:Popular Science Monthly Volume 63.djvu/340

336

substance of the Leguminosæ. In some cases the bacteria can also be prepared for transport in fluid cultures. The colonies in the agar-gelatin are distributed in water, together with the agar-gelatin, by the user (after removing the stopper) in the proportion, for example, of the contents of one glass tube to from one to three liters of water, which is previously mixed with a suitable material, such as an aqueous extract of the green substance of Leguminosæ sugar asparagin, for propagating the bacteria. This propagating material is delivered with the bacteria tubes. Preferably the glass tube is laid in the water until the agar-gelatine is dissolved.

Immediately before sowing, the whole of the emulsion prepared as above mentioned is poured over the seeds. The amount of water added for each kind of seed is so proportioned that after the seeds have been thoroughly and uniformly moistened by a careful working over by hand, a surplus of liquid will still remain. For clover-seed, for example, for twenty kilograms of seed the admixture of three liters of water with the contents of three glasses of inoculating material (each glass containing, for instance, three cubic centimeters agar-gelatin with pure cultures) is sufficient. For more bulky seeds a somewhat larger amount of water is required. A sufficient quantity of dry sand or earth from the field to be sown is then gradually added with careful stirring, until the body of seed is in a suitable condition for sowing by hand or by means of a sowing machine.

This microbic (rhizobic) soil fertilizer for leguminous plants was given the commercial name 'nitragin,' and its efficiency was quite carefully and extensively tested and commented upon by European and American investigators. The consensus of opinion seemed to be that it was of doubtful practical utility for agricultural purposes. Some authorities maintained that it was of unquestionable value in virgin soil. In rich and otherwise favorable soil conditions it is of only slight value. It is maintained that nitragin aids very materially in developing and ripening the fruit. As becomes evident from careful consideration, the value of this microbic fertilizer depends upon whether it will cause an increased development in the number and size of root tubercles over and above those which would develop without the presence of this artificial aid. If the soil is already well supplied with rhizobia or root tubercle bacteria, as soil naturally would be if the leguminous plants under consideration had been grown in it for one or more seasons, nitragin would in all probability be of little or no value. In any case the anticipated practical results have not been realized, as I am informed by a letter from Victor Koeehl & Co. of New York City which states that 'nitragin is withdrawn from the market and is no longer manufactured.'

A second and later improvement in the method of inoculating seeds with root tubercle bacteria (rhizobia) is given by Hartleb in the following specifications forming part of letters patent No. 674,765, granted May 21, 1901, at Washington, D. C.:

Be it known that I, Richard Hartleb, a citizen of Germany, residing at the Botanisches Institute der Hochschule, Aachen, in the Empire of Germany, have