Makers of British botany/Sir Joseph Henry Gilbert 1817—1901
Early training in Chemistry—his meeting with Lawes—official distinctions—the Lawes-Gilbert combination—the Rothamsted Reports—Liebig's 'mineral theory'—the relation to nitrogen—Leguminous plants—Hellriegel and others—confirmation of their results—nitrification—feeding of stock.
Joseph Henry Gilbert was born at Hull on August 1, 1817. He was a son of the manse being the second son of the Rev. Joseph Gilbert, a Congregational Minister. His mother was one of the gifted daughters of the Rev. Isaac Taylor of Ongar, and a well-known writer of hymns and songs for children. Whilst at school young Gilbert had the misfortune to meet with a gunshot accident which deprived him of the use of one eye, a mishap which for a time threatened to mar his future career, but his own inherent determination and the home-training of the manse enabled him to overcome the disadvantage of defective eye-sight, and triumph over physical disability.
From school he went to Glasgow University and studied chemistry under Professor Thomas Thomson, then to University College, London, where he attended the classes of Professor Graham and others, and worked in the laboratory of Professor Todd Thomson. Here it was, in Dr Thomson's laboratory, that he first met Mr J. B. Lawes, with whom he was afterwards so intimately associated. He then proceeded to Giessen for a short time, studying under Liebig and taking his degree of Doctor of Philosophy in 1840. Returning to London, he worked at University College, acting as laboratory assistant to Professor Thomson, and became a Fellow of the Chemical Society on May 18, 1841, when the Society was barely three months old. He then left London to take up calico printing and dyeing in the neighbourhood of Manchester, but returned south in 1843, at the invitation of Mr Lawes, to assist in the agricultural investigations at Rothamsted, Herts.
Mr John Lawes had begun experiments in 1837 on growing plants in pots with various manures. He discovered the fact that mineral phosphates when treated with sulphuric acid yielded a most effective manure. Taking out his patent for the production of superphosphates in 1842, Lawes soon found himself busy with the establishment of a successful business. Not wishing to give up the agricultural investigations which he had commenced in the fields of Rothamsted he decided to obtain scientific assistance, and remembering the young chemist he had met in Dr Thomson's laboratory, Gilbert was invited in June 1843 to superintend the Rothamsted experiments. Thus began that partnership in investigation which has yielded such a rich harvest of results, and an association with Rothamsted which lasted for fifty-eight years.
Gilbert was elected a Fellow of the Royal Society in 1860, and received a Royal Medal in 1867. He was President of the Chemical Section of the British Association in 1880, and President of the Chemical Society, 1882-3. In 1884 he was appointed Sibthorpian Professor of Rural Economy at Oxford, and held the chair until 1890. He was a member of various foreign academies and societies, and was the recipient of honorary degrees from several home universities, becoming LL.D. of Glasgow (1883), M.A. of Oxford (1884), LL.D. of Edinburgh (1890), and Sc.D. of Cambridge (1894). In 1893 on the occasion of the jubilee of the Rothamsted experiments he received the honour of knighthood.
The character and scope of Gilbert's life-work was well described by Prof. Dewar at a special meeting of the Chemical Society in 1898, when he said, "The work of Gilbert, as we know, was early differentiated into that most complex and mysterious study, the study of organic life. For the last fifty years he has devoted his attention to the physiology of plant life in every phase of its development. With a skill that has been unprecedented, he has recorded from year to year the variations in the growth of every kind of nutritious plant. He has examined into the meteorological conditions, the variations of climate, of soil, and of mineral agents, of drainage, and of every conceivable thing affecting the production and development of plant growth. These memoirs are admitted throughout the world to be unique in their importance. Wherever the chemist or the physiologist, the statistician or the economist has to deal with these problems, he must turn to the results of the Rothamsted experiments in order to understand the position of the science of our time. These results will be for ever memorable; they are unique and characteristic of the indomitable perseverance and energy of our venerated President, Sir Henry Gilbert."
The close association of Lawes and Gilbert in the Rothamsted experiments makes it almost impossible to separate the work of the two men. The majority of the 132 papers issued from Rothamsted between 1843 and 1901 appeared under the joint names of Lawes and Gilbert, and it would be as difficult as it is undesirable to attempt an analysis of this partnership. It was essentially a partnership devoid of any jealousy, and actuated by a feeling of mutual regard and esteem. There never was a question as to the "predominant partner." The two workers formed an unique combination, each supplying some deficiency in the other. Lawes possessed the originating mind and had a thorough knowledge of the facts and needs of practical agriculture; Gilbert was the exact scientist, the man of detail and method. Dr J. A. Voelcker, who speaks of Gilbert as his life-long friend and teacher, says, "The partnership and collaboration of 'Lawes and Gilbert' represented an excellent embodiment of the motto 'Practice with Science.' Lawes was essentially the practical agriculturist quick to see and grasp what the farmer wanted, and to become the interpreter to him. He was the man to whom the practical farmer turned, the one to write a brisk article on some subject of agricultural practice or economy, to answer a practical question, or to solve some knotty problem. Lawes was the more versatile of the two, the more inclined to introduce changes in and modifications of the original plan; and he has been known to say, jokingly, that if he had been left to have his own way, he would have ploughed up many of his experimental plots before they had yielded the full results, which continuance on the old lines alone brought out. Gilbert, on the other hand, was possessed of indomitable perseverance, combined with extreme patience and careful watching of results. His was the power of forecasting, as it were, what might, in the end, lead to useful results. With the determination to carry out an experiment to the very close he united scrupulous accuracy and attention to detail. Gilbert, it may be said, was not so much the man for the farmer, but for the scientist, and he it was who gave scientific expression to the work at Rothamsted, and who established field experiments on a scientific basis in this country."
To describe in detail Gilbert's work it would be necessary to write an account of the Rothamsted experiments, a task beyond our present limits seeing that the collected reports occupy nine volumes.
The last published "Rothamsted Memoranda" gives a list of 132 papers. They are divided into two series, one relating to plants, the other to animals.
Series I. deals with "Reports of Field Experiments, Experiments on Vegetation, &c., published 1847—1900 inclusive," and contains 101 papers. These reports on plants are concerned chiefly with the results obtained by growing some of the most important crops of rotation separately, year after year, for many years in succession, on the same land without manure, with farm-yard manure, and with various chemical manures, the same description of manure being, as a rule, applied year after year on the same plot.
Amongst the numerous field experiments conducted on these lines one of the most interesting is the field known as Broadbalk field, in which wheat has been grown continuously for over 60 years. The results show that wheat can be grown for many years in succession on ordinary arable land if suitable manure be provided and the land be kept clean. Even without manure of any kind the average produce for 46 years—1852 to 1897 was nearly 13 bushels per acre, about the average yield per acre of the wheat lands of the world. On this field it was found that mineral manures alone gave very little increase, whilst nitrogenous manures alone gave a much greater increase than mineral manures alone, but the mixture of the two gave much more than either alone. It is estimated that the reduction in yield, due to exhaustion, of the unmanured plot over 40 years—1852 to 1891—was, provided it had been uniform throughout, equivalent to a decline of one-sixth of a bushel per acre. It is related that a visitor from America, when being shown over the Broadbalk field, said to Sir John Lawes, "Americans have learnt more from this field than from any other agricultural experiment in the world."
Another set of field experiments of exceptional interest is that relating to the "Mixed Herbage of Permanent Grass Land." The land was divided into twenty plots. Two plots have received no manure from the commencement of the experiment, two have received a dressing of farm-yard manure each year, whilst the remainder have each received a different kind of artificial or chemical manure, the same kind being applied year after year on the same plot, except in a few special cases. Repeated analyses have shown how greatly both the botanical constitution and the chemical composition of the mixed herbage varied according to the kind of manure applied.
The results of these experiments were given under three headings—agricultural, botanical and chemical, and show in an exceptional manner the care of detail to which every investigation was subjected by Gilbert. Some people have thought that this minute attention to detail was carried to excess by Gilbert, and resulted in a bewildering multiplication of numerical statements and figures. One can, however, but admire his love of accuracy and absolute conscientiousness, and if his caution appeared at times to be carried to an extreme, the result has been to make "the Rothamsted experiments a standard for reference, and an example wherever agricultural research is attempted."
One of the most important results of the Rothamsted investigations has been the replacing of the "mineral theory" of Liebig by the "nitrogen theory" of Lawes and Gilbert. Liebig held the view that each crop requires certain mineral elements from the soil, and that crops will not flourish where the appropriate elements are lacking. Every soil contains some element in the minimum. Whatever element this minimum may be it determines the abundance and continuity of the crop. The only fertiliser which acts favourably is that which supplies a deficiency of one or more of the food elements in the soil. The atmosphere, according to Liebig, supplies in sufficient quantity both the carbon and nitrogen required by crops, and the function of manure is to supply the ash constituents of the soil. The exhaustion of soils is to be ascribed to their decreased content of mineral ingredients rather than to decrease in nitrogen.
When careful study of the composition of the atmosphere proved that the amount of ammonia brought down to the earth by rain scarcely exceeds a few pounds per acre annually, Liebig maintained that plants are capable of directly absorbing ammonia by means of their leaves. He pointed out that the beneficial effects of nitrogenous manures are most apparent in the case of cereal crops with a comparatively short vegetation period, and least apparent in the case of leafy crops with a long vegetation period. The long vegetation period of crops like clover allowed time for the utilisation of the ammonia of the air and no artificial supply was necessary. On the other hand, crops with a short vegetation period had a limited time for accumulating ammonia from the air, and responded readily to applications of nitrogenous manures.
Gilbert, early in his work at Rothamsted, noticed that the results of his field experiments were at variance with this "mineral theory," as it was called, of Liebig, and soon found himself involved in a controversy with the great German chemist which was not always free from bitterness. He found that the nitrogen compounds of the atmosphere were sufficient only for a very meagre vegetation. Cereals treated with ammonium salts and other nitrogenous manures showed a far greater increase of produce than when phosphates, potash or other ash constituents only were supplied. "As more nitrogen was assimilated a greater amount of the fixed bases were found in the ash, and he considered that the function of the fixed bases was to act as carriers of nitric acid. These bases potash, soda, lime and magnesia, were not mutually replaceable, but the predominance of one or the other affected the produce. Luxuriance of growth was associated with the amount of nitrogen available and assimilated, and in the presence of this sufficiency of nitrogen the formation of carbohydrates depended on the amount of potash available." The possibility that the free nitrogen of the air might supply the nitrogenous needs of plants was disproved by growing plants in calcined soil and removing all traces of ammonia from the air before it was admitted into the glass case in which the plants were growing. Determinations were made of the nitrogen in the seed and soil at the beginning of the experiments, and in the plants and soil at their conclusion.
The work on the assimilation of nitrogen by plants extended over three years and was made the subject of a communication to the Royal Society in 1861. The paper, entitled, "The Sources of the Nitrogen of Vegetation; with special reference to the question whether Plants assimilate free or combined Nitrogen," occupies 144 pages of the Philosophical Transactions, and is a brilliant example of the scrupulous accuracy and attention to detail which characterised all Gilbert's work. It is divided into two parts—I. "The General History and Statement of the question."—II. "The Experimental Results obtained at Rothamsted during the years 1857, 1858 and 1859." The authors state in the summary of conclusions that "in our experiments with graminaceous plants, grown both with and without a supply of combined nitrogen beyond that contained in the seed sown, in which there was great variation in the amount of combined nitrogen involved and a wide range in the conditions, character and amount of growth, we have in no case found any evidence of an assimilation of free or uncombined nitrogen.
"In our experiments with leguminous plants the growth was less satisfactory, and the range of conditions possibly favourable for the assimilation of free nitrogen was, therefore, more limited. But the results recorded with these plants, so far as they go, do not indicate any assimilation of free nitrogen. Since, however, in practice leguminous crops assimilate from some source so very much more nitrogen than graminaceous ones under ostensibly equal circumstances of supply of combined nitrogen, it is desirable that the evidence of further experiments with these plants under conditions of more healthy growth should be obtained."
As long as Gilbert's investigations were confined to non-leguminous plants and to leguminous plants grown in calcined soil the "nitrogen theory" was triumphant. When, however, leguminous plants were grown in uncalcined soil or in the open the results were uncertain, and in many cases the manures supplying ash constituents alone proved the most effective. The elucidation of these uncertain results has been a tedious problem, and has taken many years of patient investigation, but gradually the evidence accumulated which led to its solution.
Field and pot experiments in Germany, France, England and the United States in the late seventies and early eighties furnished abundant proof that under certain conditions leguminous plants do obtain nitrogen from the atmosphere, and gradually, from the work of Rautenberg, Frank and others, the idea was evolving that fungi or micro-organisms play some important part in the process.
Gilbert, however, would not listen to any such heresy, as he considered that the question of the assimilation of the free nitrogen of the air by plants had been finally settled by the experiments of 1857-60. It was therefore a most happy chance that Gilbert was present at the scientific congress in Berlin in 1886 when Hellriegel described his experiments on leguminous plants, showing that the formation of nodules on these plants was associated with the fixation of atmospheric nitrogen. In commenting subsequently on these experiments, Gilbert said, "It must be admitted that Hellriegel's results, taken together with those of Berthelot and others, do suggest the possibility that, although the higher plants may not possess the power of directly fixing the free nitrogen of the air, lower organisms, which abound within the soil, may have that power, and may thus bring free nitrogen into a state of combination within the soil in which it is available to the higher plants—at any rate to 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 maybe 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 their experiments on pigs that fat was undoubtedly produced from carbohydrates. The German physiologists doubted this, and for some time there was a wordy warfare between the rival camps. Gradually the experimental evidence for the formation of fats from carbohydrates became overwhelming, and once again the Rothamsted position was vindicated.
Gilbert maintained throughout his life a close connection with foreign workers, and his holidays were frequently employed in visiting institutions and attending scientific meetings on the Continent. He made three visits to the United States and Canada and delivered several lectures there.
As he passed into old age his powers seemed to suffer little diminution, and his appearance at the age of eighty showed little indication of physical weakness. The death of Sir John Lawes in August 1900 was a severe blow to him, and soon afterwards his energies began to fail. He had a severe illness whilst away in Scotland in the autumn of 1901, but he recovered sufficiently to be able to return to his work for a short time. With the indomitable tenacity which had characterised him throughout life he continued actively at work for a few more weeks, eventually succumbing on December 23rd, 1901, in his eighty-fifth year.
Thanks are due to Dr J. A. Voelcker for kind assistance; and to the Royal Agricultural College Students' Club, Cirencester, for permission to reproduce the accompanying photograph.