yo Massee : The Action of Bacteria on Higher Plants. 



The use of artificial manures in which a considerable amount 

 of free acid is present, is very injurious, as stated above, for 

 the reason that acid actually checks the work of Bacteria. 

 When such manures are once used their continuance becomes 

 almost imperative, as the natural fertility of the soil, induced by 

 Bacteria, is to a great extent destroyed, and the fertility of the 

 soil, kept up by the use of artificial manures, is a costly process, 

 and only justifiable in the case of rapidly-g-rown crops, as 

 tomatoes, cucumbers, etc., where heat, temperature, fertilisers, 

 etc., are broug^ht to bear all at once to rush a crop. This, how- 

 ever, is horticultural gambling. 



It has recently been shown that there is also present in 

 the soil a group of organisms called denitrifying Bacteria, which 

 exactly undo the work done by the nitrifying Bacteria. In other 

 words, they decompose nitrates, setting free nitrogen, ammonia, 

 etc., which escapes into the air, and thus for the time being 

 cannot be used as plant food. These forms, however, are few 

 in number as compared to the nitrifying Bacteria, and green 

 plants consequently do not suffer materially from their activity, 

 although under certain conditions manure heaps may be 

 rendered almost useless owing to their presence. 



Saltpetre or nitre (nitrate of potash), whether produced 

 naturally as in certain parts of India, or artificially in a salt- 

 petre manufactory, owes its origin to work done by a very 

 minute Bacterium called Nitrohacter. This species is only about 

 0.5 /X long, and, furthermore, is the only known living organism 

 that can assimilate carbonic acid in darkness. Like the other 

 nitrifying Bacteria it is aerobic. 



The requisites for the production of saltpetre are the 

 presence of decomposing animal remains, carbonate of potash, 

 and moisture. The Bacteria first liberate ammonia from the 

 organic remains ; this is further converted by stages, first into 

 nitrous acid, then into nitric acid. Finally the nitric acid takes 

 the place of the carbonic acid in the carbonate of potash, and 

 nitrate of potash, or saltpetre, results, a salt soluble in water 

 and from which green plants can obtain nitrogen. 



The enormous deposits of saltpetre met with in the arid 

 region of Peru were not originally formed there, but carried in 

 solution from the surrounding country, and left in a solid form ^ 

 after the disappearance of the water. 



It has been known for ages that a crop of leguminous plants, 

 as peas, beans, tares, etc., enriched the soil in w-hich they grew; 



Naturalist, 



