BY R. GRBIG-SMITH. 291 



of the salt. Organic salts such as citrates, tartrates or succinates 

 enable a luxuriant slime to be formed, but they do not enable 

 differences to be exhibited between the races. Phosphates, 

 although they do not as a rule assist the formation of so luxuriant 

 a slime, yet bring out certain racial peculiarities in response to 

 the nutrients. With certain races, small quantities of dextrose 

 in the presence of citrate nearly prohibit the formation of slime 

 from saccharose. With other races, and in the presence of phos- 

 phate, the addition of dextrose to saccharose increases the yield. 

 The action of levulose is peculiar. Some races produce slime 

 from it while others do not. Lupin (Krai) race makes slime 

 from this sugar in the presence of phosphate, but not of citrate 

 or other organic salt. The general inability of the races to form 

 slime from levulose appears to depend more upon the individual 

 acid which is also produced than upon the acidity. 



The most suitable sources of nitrogen are asparagin and nitrate; 

 ammonium salts are bad, while peptone and urea are variable. 

 As a rule the optimum percentage of asparagin in the medium 

 varies from 0-04 to O08, but in the case of Robinia the yield of 

 slime was proportional to the asparagin added. 



The quantity of saline matter required in the formation of 

 slime is small, from 0T % to 0*2 % is enough, and like the 

 optimum quantity of nitrogen, this approximates to what is 

 found in soil water. 



As a rule the optimum temperature is 22°C. An exception is 

 the race obtained from Robinia pseudacacia, which has an 

 optimum of 26°. 



The most favourable reaction for the medium depends upon 

 the kind of salt which may be present; a neutral reaction is best 

 with organic salts and an alkaline with phosphates. An exception 

 was found in an acidophile race which was obtained from the 

 Blue Lupin. 



The experiments upon the physiological activities of the 

 various races of the micro-organism show that, after their isolation 

 from the nodules, they are all different. How they may have 

 behaved before they had been subjected to the individual juices 



