Page:Makers of British botany.djvu/293

 Rh members of the Papilionaceous family. At the same time, it will be granted that further confirmation is essential before such a conclusion can be accepted as fully established."

This comment reveals the essential conservatism of Gilbert's mind, but the true greatness of the man is seen when we find him, at the age of seventy, repeating the experiments of Hellriegel and Wilfarth, and himself supplying the confirmation of their results which he considered essential.

The results of these experiments, contributed to the Royal Society in 1887, 1889, and 1890, fully confirmed the theory that leguminous plants are able to assimilate the free nitrogen of the air by means of the micro-organisms contained in their root nodules, and also explained the failure in the 1857-60 experiments to demonstrate nitrogen fixation by leguminous plants owing to the use of calcined soil by which the inoculating organisms present in the soil were destroyed.

Gilbert's investigations from 1871—75 showing that the drainage waters from the experimental fields of Rothamsted contained more nitrates as the amount of ammonium salts applied to the soil increased, have been quoted by some writers as being the basis of the modern theory of nitrification. It must be remembered that Gilbert was at first actively hostile to the bacterial theory of nitrification, and the credit and honour of the work done at Rothamsted on the nitrifying organisms belongs entirely to Warington.

A few words must suffice for an account of the series of Rothamsted experiments on animals. Series II deals with "Reports of experiments on the feeding of animals, sewage utilisation, &c. Published 1841—1895 inclusive," and contains 31 papers. Among the points investigated may be mentioned—the composition of foods in relation to respiration and the feeding of animals; experiments on the feeding of sheep and the fattening of oxen; some points in connection with animal nutrition; the feeding of animals for the production of meat, milk and manure.

The work on the part played by carbohydrates in the formation of animal fat led to a keen controversy with foreign investigators. Lawes and Gilbert had satisfied themselves by