[Vol. 6 



6 ANNALS OF THB MISSOURI BOTANICAL GARDEN 



In further confirmation of his theory Sohngen measures the 

 oxygen and nitrogen adsorbed by colloidal silica and colloidal 

 ferric oxide. He finally concludes that for luxuriant develop- 

 ment of Azotobaeter in Beijerinck's medium only nitrogen 

 and oxygen are lacking. By the use of the colloids described 

 by him there occurs a direct contact between the bacteria and 

 oxygen and nitrogen, with the result that luxuriant growth of 

 Azotobaeter takes place in the culture medium. 



Still another theory has been proposed by Bottomley ( '14) 

 to account for growth stimulation in cultures of Azotobaeter 

 and nitrifying bacteria. Marked acceleration of growth of 

 these bacteria and of wheat seedlings was obtained by him 

 by the use of extracts of "bacterized" peat, i. e., peat which 

 had been inoculated with certain aerobic bacteria and incu- 

 bated for a suitable time under favorable conditions as to 

 temperature and moisture. He later ('15) proposed the term 

 "auximones" for these accessory substances, which he be- 

 lieved were analogous to the "vitamines" of animal physi- 

 ology. Bottomley 's associate, Miss Mockeridge ('17), studied 

 in some detail the action of these extracts of bacterized peat, 

 and believed that * ' auximones ' ' had been responsible for the 

 marked results obtained by Krzemieniewski on the addition of 

 humus to cultures of Azotobaeter. Bottomley ('17) claims to 

 have isolated a nucleic acid derivative from " bacterized ' ' 

 peat and suggests that it is of importance in the results ob- 

 tained on accelerated growth. 



Very recently Bonazzi ('19) has obtained results on the 

 growth of nitrifying bacteria that are very much to the point 

 on this general problem. Intensive growth as measured by one 



physiological activity was obtained in case of Nitrosococeus 

 (the nitrite-producing bacteria) when the solution was prop- 

 erly stirred mechanically. The nutrient medium was of very 

 simple composition, so that the possibility of " auximones ' ' 

 and "rare elements*' would be eliminated. It was also soon 

 observed that this type of treatment was distinctly beneficial 

 for the growth of Azotobaeter. Aside from mentioning that 

 the shaking possibly produced better aeration or assisted in 

 the removal of by-products, Bonazzi did not enter into any 



