SUMMARY. 25 



the sulphate greatly increase the quantity of sulphuric acid in the 

 ash. The carbonate would seem to be an ideal form in which to 

 supply the potash for combining with the* organic acids in the plant, 

 and its use has generally been found to improve the burning quali- 

 ties. But, aside from the high cost of this material, there are other 

 serious objections to its use, for it has a very strong alkaline reaction, 

 and it seems probable that when used in large quantities it will 

 eventually injure seriously the productiveness of the soil. The sili- 

 cate is free from these objectionable properties, and if the potash 

 can be made available there is every reason to believe that this will 

 prove to be a very valuable source of potash for tobacco. 



The sum of the lime and the magnesia in tobacco does not, as a 

 rule, vary widely ; or, in other words, the greater the amount of lime 

 the less will be the amount of magnesia, and vice versa. The appli- 

 cation of fertilizers containing magnesia increases the percentage of 

 this element in the tobacco, but when used in the form of the car- 

 bonate the injury to the burning qualities would be reduced to a 

 minimum. It is believed, however, that the use of fertilizer salts 

 containing magnesia in the form of sulphate is inadvisable. 



The percentage of organic nitrogenous compounds, including nico- 

 tine, is generally proportional to the luxuriance and vigor of growth ; 

 hence tobacco of very rank growth contains excessive quantities of 

 these constituents. Again, these substances are most abundant when 

 the plant is, as a whole, growing most rapidly, and also in the most 

 rapidly growing parts of the plant. Conditions favorable to rank 

 growth are brought about by the use of excessive quantities of nitroge- 

 nous fertilizers, especially when the nitrogen is in readily available 

 forms. The chief danger from this source, however, lies in the appli- 

 cation of quickly available forms of nitrogen during the later stages 

 of growth, thus preventing or delaying the normal ripening of the 

 leaf. Since the percentage of albuminoids decreases rapidly through- 

 out the ripening process after the leaf has reached its full growth, 

 this is an important reason why tobacco should not be harvested 

 until the leaf is well ripened. 



105 



