11 r M IS — 11 LMOC.KN. 245 



(Occasionally and ensured the infection of the r(jol> by the nodule 

 bacteria, they could turn their backs on the ueed for manurin<j[ 

 with expensive nitroj^enous manures. But everything did not 

 turn out so simple as had been expected. Many faihu-es have 

 been experienced in endeavours to produce a successful inocu- 

 lation of the roots of the legumes; but it is not ])ossible to discuss 

 these here. 



Mention should be made of the fact that the radicicola group 

 is not the only nitrogen fixing group of organisms. There are 

 the azotobacter organisms which live in the soil and assimilate 

 nitrogen from the soil air just as the other group does, but with 

 this exception, that they do not live on the roots of plants. The 

 Azotobacter group obtains its carbonaceous food from the ])lant 

 residues in the soil ; likewise its mineral salts. Tt obtains no- 

 thing from the living plant. 



The gain in nitrogen due to the azotobacter organisms is very 

 considerable, provided the soil conditions are suitable. These 

 are an adequate air and moisture supply, together with plenty 

 carbonaceous material, mineral sailts and calcium carbonate; 

 the latter evidently to ensure that the carbonaceous matter shall 

 be present, in part, as soluble humus, the iiiaficre noire dc 

 Grand can. 



Bottomley seems to have come to the conclusion that the 

 ideal in soil inoculation would be to add both groups of bacteria 

 to the soil in a medium 'that would provide them with food, and 

 thereby render tliem independent of suitable soil conditions. Ni- 

 trogen fixation would, under such conditions, proceed whether 

 radicicola infected the roots of legumes or not, because both 

 grou]3S would be active in the soil by reason of a bountiful food 

 supply, provided only suitable air and moisture conditions 

 prevailed. 



Bottomley, therefore, searched for a medium that would 

 suit both radicicola and azotobacter groups, and at the same time 

 ])lace them in cfrcumstances in which they would be as inde- 

 ])endent of soil conditions as possible. Such a medium would 

 be one rich in soluble humus [because of the latter's richness in 

 carbonaceous matter, and because of its colloidal properties, 

 which would keep the organisms well supplied with mineral salts. 

 The alkalinity of such a medium would, moreover, be very fa- 

 vourable to both organisms]. 



Well-rotted farmyard manure would fulfil these conditions, 

 but its great bulk was against it. Bottomley, therefore, fell back 

 on peat, which he treats as follows : — 



The peat is infected with certain aerobic bacteria, and kept 

 moist at a temperature of 26° C. for about a week. Steam is 

 then forced through the mass to sterilize it. A sterile, neutral, or 

 slightly alkaline mass is the result. The material is very rich 

 in soluble humus, as will be seen from the table given below. 

 The sterilized, bacteriallv changed peat is then infected 

 with cultures of radicicola and azotobacter organisms, and kept 



