4 PRESIDENTS ADDRESS. 



deposition of the agricere by the solvent is greatest in the 

 upper layers of the soil, and in these layers the bacterial 

 increase is less than in the lower defatted strata. Other 

 cognate matters were investigated, and it was shown that 

 heavy rains wash the soil-toxins into the subsoil. 



The number of nodule-forming bacteria in the soil was also 

 investigated. That the nodule-organism of leguminoiis plants 

 is capable of fixing atmospheric nitrogen while free in the 

 soil, is generally admitted, but the fixation is chiefly credited 

 to the Azotobacter group of bacteria. This is mainly because 

 it is presumed that the normal place for the anabolic changes 

 effected by the nodule-former is in the nodular tissue of legu- 

 minous plants. They were not thought to be very numerous 

 in soil, and the only investigations that had been made re- 

 vealed but a few hundreds. By a special method of cultiva- 

 tion, Dr. Greig-Smith has shown that they are very numerous 

 in agricultural soils, ranging up to two or three millions per 

 gram. This considerably modifies our ideas regarding the 

 capacity of the organism for fixing free nitrogen. From their 

 numbers in soils, there is every probability that the nodule- 

 former is responsible for the major part of the gain of com- 

 bined nitrogen, which the soil continually receives. The 

 subject of the relationship of this microbe to the plant is 

 interesting and is at present under investigation. The num- 

 bers, that are in soils, vary according to the soil, the better 

 soils containing more, the poorer less; and it is possible, by 

 estimating their number, to compare the fertility of two or 

 more soils. The comparatively large number of these bacteria 

 in soils has been recently (November 11th, 1911) confirmed by 

 Millard, who, in one case, found two and one-half millions in 

 a gram of soil. 



One who works with soil-bacteria knows that manv of them 

 are gum-formers, and, as their typical faculty is pronounced 

 when they are obtained, it would appear that bacterial gums 

 are to be found in soils. The matter was tested, and evidence 

 of the presence of these substances in soil was shown. 



