PLANT NUTRITION. 17 



and sulphur. The latter comprise saltc 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 combina- 

 tion 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 " Bac- 

 teria," 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 farm- 

 yard 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 brewer uses his yeast to secure the 

 conversion of starch into sugar, and the chemist "seeds" 

 his solutions to effect the changes he wishes to bring 

 about, and just as the gardener sows the spawn or germs 

 of mushrooms in his mushroom bed, and obtains thereby 

 a crop of succulent fungi, so the farmer may be able to 

 apply to the soil the ferment-producing germs needed to 

 change its quality, and render it available for plan^ food. 

 When we have arrived at that point, manuring will be 

 reduced to a science, and a pinch of the right material 

 will be as efficient as a torn of our present compounds, 



