[SHUTT] PRESIDENTIAL ADDRESS té 
of dry matter, than plants of other orders, but the further and astound- 
ing fact that they left the soil richer in nitrogen by their growth. 
Where did this additional nitrogen come from ? What was its source ? 
If from the uncombined, free nitrogen of the air, in what wav did the 
legumes appropriate it? For by this time it had been fairly well 
established that crops in general could only obtain the nitrogen neces- 
sary for their growth from the organized nitrogen in the soil. 
Many chemists worked on this problem, prominent among whom 
was Gilbert of Rothamsted, England, who, with Lawes, for more than 
fifty years did such magnificent work in agricultural research both in 
the laboratory and field, and placed the whole world for all time under 
a debt of gratitude; for their work above that of all others has fur- 
nished the foundation of agricultural science upon which others of all 
nations have built and still are building. Unfortunately, Gilbert just 
missed thesolution of the problem, chiefly through imperfect apparatus. 
It was a great disappointment to him. The discovery was made by 
Hellriegel and Wilfarth, who conclusively showed that the legumes 
obtained their nitrogen, or in part at least, from the nitrogen of the 
atmosphere, not of themselves, but through the agency of certain 
nitrogen-fixing bacteria in the soil, which attach themselves and 
reside in nodules or tubercles upon the roots of the legumes, passing 
on their elaborated nitrogen to their host—it appears to be a case of 
symbiosis—for the building up of its tissues of root, stem and leaf. 
Without the aid of these bacteria the legumes, like all other plants, 
must draw upon the nitrates of the soil for their supply of this import- 
ant element. As I was in England and Germany at this time (1888), 
I had an excellent opportunity of learning at first hand the various 
steps of this discovery, which, for its far reaching effects and the prac- 
tical results that have followed, must be regarded the agricultural 
discovery of the century. It is interesting to note that Gilbert sub- 
sequently repeated Hellriegel’s and Wilfarth’s work and confirmed 
their conclusions. 
The next and most logical step was the preparation of cultures of 
these useful bacteria by the bacteriologists, and these cultures are to- 
day in extensive use for inoculating the seed and soil for the growing 
of legumes in districts found to be lacking in the nitrogen-fixing or- 
ganisms. 
A further step was the discovery by the chemists that clover and 
alfalfa and many other valuable legumes would not thrive in acid- 
reacting soil, that there was no development of the nodules in such 
soils. Thus was brought in the now common practice of testing the 
soil upon which it is wished to grow a legume and the application of-; » : + 
lime or gound limestone to correct ae such be Sine ASEICA i ES 
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