76 THE CULTUKE OF FARM CROPS. 



a judicious student hesitates to form conclusions, and pa- 

 tiently repeats and verifies his experiments ; and at the last 

 when he is himself convinced of the truth of any result, he 

 is slow to declare it to the world, but watches it and tries it 

 in other ways until doubt has no longer any existence. 

 Hence the slow progress of knowledge in the true science of 

 agriculture and the caution with which farmers who are 

 following up the experiments of professional students, should 

 watch the results, and form practical conclusions therefrom. 



But the peculiar action of ammonia upon plant growth, 

 and the analogy which exists between its action and that of 

 other compounds, lead us to believe that ammonia enters in- 

 to the circulation of plants, and that the hydrogen of which 

 it contains so large a proportion, there separates from the 

 nitrogen, and combines with other organic elements which 

 enter by the roots or leaves and thus aids in producing the 

 various solid substances of which plants are constructed and 

 made up. The nitrogen is then fixed in the flowers, helping 

 to produce the bright coloring matter and the agreeable 

 odors; and to form the gluten and albumen of the seeds, 

 and other parts. These and other important considerations 

 will be more fully considered in another chapter. 



It may be exceedingly interesting to note here, the results 

 of some careful tests made by a German agricultural chem- 

 ist and experimenter, in regard to the effects of ammoniacal 

 manures upon the yield of grain and the proportion of the 

 nitrogenous substances contained in it under varying cir- 

 cumstances. A number of experimental plots were treated 

 as follows, and were sown with wheat. Then from 100 

 parts of the produce of these plots the various amounts 

 shown of gluten and starch, and the increased product, were 

 estimated. 



Gluten. Starch. Produce. 



Without manure 9.2 66.7 3 



With rotted vegetable matter only.. 9.6 65.94 5 



Cow dung 12.0 62.3 7 



Horse dung 13.7 61.64 10 



Sheep dung 33.9 42.8 12 



Night soil 33.14 41.44 14 



Dried blood 34.24 41.3 14 



Dried urine.... .. 35.1 39.3 12 



