nv U. GREIG-SMITH. 



497 



In Expt. iv., tests were made in whicli the natural acidity of 

 + 1 was augmented by the addition of pliosphoric acid in quantity 

 to produce acidities of from + 1 -2 to + 2-4, but no colonies were 

 f)btaincd. From the considei'ation of Expts. iii. and iv., it is 

 evident that, unless carbonate of soda is arlded, there is no growth, 

 and that the addition of even one drop causes the medium to be 

 exceedingly favourable to the growth of Rhizobia. 



The higher numbers obtained in the absence of methyl-violet 

 in Expt. iv., led to a set being tested without it. The result 

 showed that its addition was unnecessary, and it was not used 

 again. 



Experiment v. 



A series of plates with increasing amounts of normal phosphoric 

 acid and of carbonate of soda was prepared, and smeared with 

 suspensions of soil No.l. The plates containing the acid were 

 sterile, and are not recorded. 



Experiment vi. 



^C^ 





'*i.»'^ 



