X TALKS ON MANUKES. 



Mining for coal is a very simple matter, but how l«est to get 

 the greatest quantity of plant food out of the soil, withtlie least 

 waste and the greatest fjroftt, is a much more complex and 

 difficult task. Plant food consists of a dozen or more dilferent 

 substances. We have talked about thom in the i)ages of this 

 l)Ook, and all I wisli to say here is that some of them are much 

 more abundant, and more readily obtained, than others. Tiie 

 three substances most difficult to get at arc: nitric acid, phos- 

 phovic acid and potash. All these substances are in the soil, 

 but some soils contain much more than othei*s, and tht-ir rela- 

 tive proportion varies considerably. The substance which is of 

 till' greatest importance, is nitric acid. As a rule, the fertility 

 of a soil is in proportion to tlie amount of nitric acid which 

 betcomes availal)le for tlie use of plants during the growing 

 season. Many of our soils contain large (juantities of nitrogen, 

 united with carbon, but tlie iihmts do not take it up in this 

 form. It has to be converted into nitric aeid. Nitric acid con- 

 sists of seven ])oiinds of nitrogen and twenty jioumls of 

 oxygen. It is produced by the comlmstion of nitrogen. Since 

 these "Talks" were published, several important facts have Imvu 

 discovered in regard to how plants take up nitrogen, and es- 

 pecially in regard to how organic nitrogen is converte<l into 

 nitric acid. It is brought about through the action of a minute 

 fungoid plant. Therj are several things necessary for the 

 growth of this plant. "We must have some nitrogenous 8ul>- 

 stance, a moderate degree of heat, say from seventy to one 

 hundred and twenty <legrees, a moderate amount of moisture, 

 and plenty of oxygen. Shade is also favorable. If too hi>t or 

 too cold, or too wet or too dry, the growth of the plant is 

 checked, and the formation of nitric acid suspended. The 

 presence of lime, or of some alkali, is also necessary for the 

 growth of this fungus and the production of nitric acid. The 

 nitric acid unites with the lime, and forms nitrate of lime, or 

 with soda to form nitrate of soda, o/ with potash to form 

 nitrate of potash, or salt-petre. A water-logged soil, by exclud- 

 ing the oxytren, destroys this plant, hence one of the advan- 

 tages of underdraining. I have said that shade is favorable to 

 the growth of this fungus, and this fact explains and confirms 

 the common idea that shafle is manure. 



The great object of agriculture is to convert the nitrogen of 

 our soils, or of green crops plowed under, or of manure, into 

 nitric acid, and then to convert this nitric acid into profitable 

 products with as little loss as possible. Nitrogen, or rather 



