312 ADDENDUM. 



vegetable substances, that we are not to suppose that Wheat and 

 other kinds of Corn require more nitrogen, than do the herbaceous 

 plants raised for the support of cattle. The following table shows 

 the proportion of nitrogen to carbon in the entire plants of dif- 

 ferent species ordinarily cultivated. 



With every 1,000 pounds of carbon, we obtain 



From pasture-land, in Grass 32*7 pounds of carbon. 

 From cultivated fields, in Wheat 21 '5 

 Oats 223 



Rye 15-2 



,, Potatoes 34-1 



Beetroot 39'1 



Clover 44 

 Peas 62 



The proportion of nitrogen is much greater in the seeds of the 

 Corn-plants, in which is concentrated most of the azotised matter, 

 which is elsewhere diffused through the entire structure. It is by 

 far the highest in Peas and Beans ; which are nevertheless grown 

 advantageously between Wheat-crops, and which do not require 

 any animal manure thus showing that they do not exhaust the 

 soil of its azotised matter. But the general principle formerly 

 stated (. 213), respecting the influence of manures, which readily 

 yield carbonic acid and ammonia, in accelerating the growth of 

 plants, and rendering it more luxuriant, is not affected. Still the 

 manures which are richest in this respect will be totally ineffica- 

 cious, if there be not at the same time an ample supply of the 

 mineral ingredients, which the particular species of plant requires. 



It has been mentioned (. 200 207) that the chief of these 

 ingredients are Silex, the Alkaline Carbonates, and Phosphate of 

 Lime ; and recent observations show, that it is chiefly in affording 

 an increased supply of the two first, that the good effects of burn- 

 ing a stiff clayey soil, and of manuring it with lime, two processes 

 which have long been advantageously practised, really consist. 

 Owing to the habit which prevails in this country, of allowing the 

 excrements of man to run to waste, instead of committing them 

 again to the soil, a very large quantity of phosphate of lime is con- 

 tinually being withdrawn from it ; and if it were not for the great 

 importation of bone-earth from foreign sources, the amount of corn 

 grown in this country would rapidly diminish, for want of this 

 most important ingredient. It has been suggested by Professor 

 Liebig, that the large beds of fossil excrements (coprolites), which 

 are found in some parts of Britain, might be advantageously 

 resorted to for the needed supply. 



