42 



DISEASES OF CROPS. 



aim, because it was discovered upon Allium cepa. It 

 grows tolerably well in sterilized nutrient agar-agar 

 (Japanese isinglass), and other cultivating media used by 

 scientists. Upon the surfaces of nutrient media, JB. 

 alia produces a bright-green pellicle, and causes certain 

 chemical changes to occur in albuminous substances. The 

 microbe is chromogenic ; i.e., it produces a pigment (of a 

 green colour), by the decomposition of the medium upon 

 which it lives. 



Fig. 16.— PniKEFACTiTE Bacteeicm or Onions {Bacterium allii). 

 A. The Bacterinm under the high powers of the microscope, 

 u. Jjactcmim alln growing on nutrient agar-agar. 



It appears that the whole function of this organism 

 is to decompose or disintegrate albuminous substances, 

 giving rise to certain products ; viz., sulphuretted hydro^ 

 gen gas (in small quantities), and a deliquescent alkaloid 

 of the following symbolic formula, Cjq H^„ N. 



Bacterium allii is possessed of great tenacity of life, 

 for after an exposure to 32'' C. (dry heat) for six months 

 the organism had not lost its vitality. Cold appears to 



