183 



bacteria is necessary to enable plants to utilise the nitrogen of the at- 

 mosphere, and that, for this reason Leguminosce may almost entirely 

 dispense with nitrogenous manuring of the soil they grow upon, and 

 in many instances even enrich the land with nitrogen, these observed 

 facts were not properly understood. 



It was well known in practice that clover and lucerne would grow 

 vigorously for a period of years without being manured, and when 

 flagging, could often be invigorated by a dressing with gypsum. This 

 tends to prove that these crops did not sicken for the want of nitro- 

 genous food, but on account of other elements becoming exhausted 

 or unobtainable for some reason from the soil. 



A palpable proof that the help of bacteria is almost absolutely 

 necessary to enable plants to assimilate atmospheric nitro;^en, is 

 afforded by the fact that seedlings, say, of peas, will not thrive unless 

 the soil contains at le:jst some traces of nitrogenous compounds ; but 

 as soon as they have made a start and have sent out, root ets upon 

 which the bacteria can form colonies, they prosper independently of 

 the presence of this food in the soil. 



During the experiments carried on in several Gferman agricultural 

 establishments it was discovered that every species of legume was 

 associated with a specially sympathetic bacterium which would not per- 

 form the office of fixing nitrogen for other species. Basel upon the 

 acquisition of tbis knowledge. Professor Nobbe, of Tharand, in Saxony, 

 is now preparing a number of pure cultures of these specific bacteria 

 for the purpose of sowing th'3m together with their respective culture 

 plants. These cultures are placed oti the murket under the name of 

 Nitragin, and for som ^ time have been undergoing and still undergo 

 practical tests regarding their efficacy of promoting the growth of 

 plants. 



It has not been definitely ascertainel how long these artificial cul- 

 tures can reriiin iheir vitality unimpaired; and. besides, in some 

 instances, adverse seasons have prevente I a defini e judgment being 

 arrived at as yet, w lether the results obtained in trial plots can be 

 maintained on a larger scale in the field. Co .s derable attention is 

 being paid to this question at the agricultural stations in Germany as 

 well as in the United States and elsewhere. 



THE DENITRIFYING BACTERIA. 



In addition to the organisms hitherto referred to, all of which are 

 pre-eminently friendly to plant-life, and thus indirectly to man. there 

 are a host of other bacteria met with in soil and water which play an. 

 important part, in connection with agriculture. 



Their action is to reduce the compound organic substances into less 

 complex combinations, or into simple elements, and in this manner 

 make them again available for plants to which otherwise they would be 

 lost, as these can utilise nothing but elements or simple compounds 

 for their nutrition. 



It is m mifest that were it not for the decomposition of the many 

 complex substances taken from the earth in the shape of plants and, 



