12 PLANT LIFE ON THE FARM. 



must, as has been said, be made to the " Chemistry of the 

 Farm " and other works for full details. Suffice it here to 

 say that certain of them, though always in relatively small 

 proportions, are essential to the life of the plant ; certain 

 others generally met with, though useful, are not indispens- 

 able. The former comprise salts of potash, magnesia, lime, 

 iron, and in addition phosphorus and sulphur. The latter 

 comprise salts of soda, silica, manganese, together with 

 chlorine and occasionally other ingredients. 



Of the salts just mentioned, the nitrates are of extreme 

 importance, inasmuch as nitrogen is an essential con- 

 stituent of protoplasm without nitrogen there can be no 

 protoplasm, without protoplasm there can be no plant. 

 The nitrogen is supplied to the plants from the soil in the 

 form either of nitrates (potassic nitrate, sodic nitrate), or of 

 ammonia salts in which the nitrogen is in combination with 

 hydrogen. The ammonia in the soil is made to combine 

 with oxygen, and thus to form nitric acid, through the agency 

 of minute organisms called " Bacteria," which, like the yeast 

 fungus, act as ferments ; and by their agency it is, as Mr. 

 Warington has pointed out, in confirmation of the researches 

 of Schloesing and Muntz, that the ammonia salts, which 

 themselves are inert, or it may be harmful, get converted 

 into useful nitrates. Ammonia salts applied to some soils 

 do no good, because the needful germs or ferment bodies 

 are not present in the soil ; but where they do exist, they 

 convert the useless into the useful, as before said. These 

 bacteria occur in all fermenting material, such as farmyard 

 dung, whose value as manure is in part accounted for by 

 their presence and agency. It is probable in the future 

 that just as the brew r er uses his yeast to secure the conver- 

 sion of starch into sugar, and the chemist " seeds " his 



