BACILLUS RADICICOLA 231 



nature of these nodule bacteria was established without doubt when 

 Beyerinck isolated them from the nodules and cultivated them further 

 on artificial media. These bacteria are now looked upon as the 

 generators of the nodules, by means of which the Leguminosce are enabled 

 to absorb nitrogen from the air and elaborate it into nitrogenous 

 compounds, albumen, etc. The bacteria are situated in the cells of the 

 inner layer of the nodule, which is known as the bacteroidal tissue, and 

 under the influence of the surrounding protoplasm are modified into 

 involution forms termed Bacteroids, rich in albumen and no longer capable 

 of reproduction. 



For further information on this subject, the reader is referred to an 

 interesting article on 'The Bacteria of Soil, with special reference to 

 Soil Inoculation,' by R. Stewart MacDougall, in the Transactions of the 

 Edinburgh Botanical Society, July 1897. 



BACILLUS RADICICOLA (BEYERINCK). 



Found in young root nodules, also in the tissues of plants. 



Microscopical Appearances. In cultures it occurs as large rods 

 1 to 4> //, long, and in small clusters or rovers 0'18 to 0'9 p- The large 

 rods frequently exhibit knotted, irregular, fork-shaped or three-armed 

 bodies. The bacteria in the nodules exhibit a similar morphology. The 

 rovers belong to the smallest of known bacteria, and can escape through 

 the pores of a Chamberland filter. 



Motility. Motile, especially the rovers, which sometimes escape from 

 the parent colonies, and found a daughter colony at a distance in the 

 gelatine. 



Spore Formation absent. 



Staining Reactions. Sections of the nodules are best stained in a 

 solution of equal parts of fuchsin and methyl-violet in 1 per cent, acetic 

 acid. The plasmal contents and membrane of the nodule cells are 

 coloured blue, the bacteria of the infection threads red, whilst the 

 membrane of the latter remains uncoloured. 



Biological Characters. These organisms grow under aerobic 

 conditions on ordinary gelatine, but very slowly. The best medium is a 

 decoction of Papilionaceae leaves or stalks, with 7 per cent, gelatine, J 

 per cent, asparagin, and J per cent, cane-sugar added. The developing 

 colonies are semi-circular, whitish or slightly clouded. The larger 

 colonies are watery, while the smaller ones are solid and adhere in one 

 piece. According to Beyerinck, the various species of Leguminosae 

 exhibit a difference in the form of the colonies and the bacteria. Kruse 

 considers that they are probably only varieties of one species. 



