Feb. 1897.] BOTANICAL SOCIETY OF EDINBURGH 27 



out of the tube on to a gelatine plate. Within a very- 

 short time the gelatine grows stiff, and holds, caught at 

 certain points, the organisms. The isolated bacteria begin 

 to grow and multiply by fission, and soon each has given 

 rise to a colony. It is taken for granted that each colony 

 has arisen from one individual germ, and by counting the 

 colonies one gets the number of germs present in the 

 1 ccm. of the earth mixed in the water, and can thus 

 calculate the number in the quart, i.e. in the gramme of 

 earth. The colonies differ in external appearance, and 

 each is confined to members of the same species. To 

 get a pure cultivation of a particular species, one removes 

 with a platinum needle a small part from a colony, and 

 inoculates a fresh gelatine tube. In general outline, then, 

 this is the method, but in very exact work other points 

 must be attended to, e.g. certain bacteria only grow in 

 absence of oxygen (anaerobic), and such must be cultivated 

 accordingly. Questions of temperature, and differences 

 in nourishing media to suit the varying bacterial tastes 

 must also be considered. 



BACTERIA OF THE SOIL. 



In the soil are a very large number of different species, 

 some of which have been investigated and proved harmful 

 or useful, but many more, as far as research has gone, 

 have not yet been proved to have any significance as 

 regards man himself or man's cultural operations. I 

 propose to choose out of the mass three sorts, all of much 

 importance to agriculturists, viz. : — 



1. The Putrefactive. 



2. The Nitrifying. 



.3. The Nodule forming Bacteria of Leguminosa?. 

 There are a number of bacteria which act on nitrogenous 

 organic compounds in the soil and cause putrefaction, 

 resolving the albuminous organic matter into simpler 

 principles. We place as manure on our land complex 

 organic substances, which by the aid of the putrefactive 

 germs are rendered simpler, and brought into conditions 

 such that they can be assimilated by the plant. When as 

 a result of the action of the putrefactive bacteria on 

 albumen, ammonia, say, is produced, this is seized and 



