49 



He concludes that aqueous exhalations from i>lauts may be effected 

 in three ways : 



1. By mseusible exhalation from the entire surface of the cuticle by means of a true 

 gaseous dialysis. 



2. By sudden emission of saturated gases which escape from the stomata when the 

 plant is submitted to a rapid elevation of temperature, especially when inclosed. 



3. By accidental exudation, resulting from a defect in the equilibrium between the 

 absorptive action of the roots and the work of the parts exposed to the atmosphere, in 

 fixing carbon combined with the elements of water, work which ceases with the dis- 

 appearance of light. 



I know that it is also right to conclude that heat exercises a strong influence upon 

 this function, and that at equal temperatures carbonic acid in presence of light has the 

 eifect of diminishing the evaporation. 



AlNOIONlA AND NITRIC ACID — THEIR RELATIVE VALUE IN AGRICUL- 

 TURE. — Dr. Hellriegel of Dahme, having had his attention particularly, 

 directly directed to the comparative influences of ammonia and nitric acid 

 upon plant growth, was led to make an extended course of investigations 

 continuing through a series of years, the results of which formed the sub- 

 ject of an interesting paper which he presented at a late meeting of the 

 Central Agricultural Society in Frankfort. His work consisted princi- 

 pally in sand and water culture experiments with different compounds of 

 ammonia and nitric acid which may be practically applied in agriculture, 

 and he has certainly obtained some very interesting and valuable results ; 

 effects of the application of the different compounds may be shown by 

 the following table : 



Kind of seed grown. 



Barley 



Do 



Do 



Sumincr-^heat 



Do 



Do 



Sathmer-rve .. 



Do...'..... 



Do 



Nitrogenous compound 

 applied. 



Amount of dry 

 substance har- 

 vested. 



Nitrate of lime 



Sal ammoniac 



None 



Nitrate of lime 



Sal ammoniac 



None 



Nitrate of lime 



Nitiate of ammonia 

 None 



^nUiijrams. 



12, 800 

 300 

 300 



22,000 

 380 

 G30 



15,000 

 720 

 810 



In case of the barley, when the nitrogen was applied to the plants in 

 the form of nitric acid they grew normally and well, but as may be seen 

 from the table when sal ammoniac was applied, no more was produced 

 than when no nitrogenous material was added. Tiie same remarks ap- 

 ply to summer-wheat and summer-rye, except that in these cases the 

 production was less when ammonia-salts were applied than when the 

 plants received no nitrogen whatever, showing that the ammonia-salts 

 seem really to have an injurious effect. It would, therefore, appearthat 

 in their decomposition the roots suffered from the deleterious influences 

 of the separation-products. In the decomposition of nitrate of lime, 

 however, nothing but carbonate of lime| which is perfectly harmless, is 

 left behind. Since it is evident, therefore, that ammonia salts faileil to 

 produce good results in sand-culture, it was considered of some import- 

 ance to make some experiments to (fetermine if it wei^ not possible to 

 devise some means by which these could be employed and be not entirely 

 lost. In order to avoid the injurious separation -j) rod ucts in question. 

 Dr. Hellriegel tried the effect of nitrate of ammonia, and as this combi- 

 nation contained two sources of nitrogen, both nitric acid and ammonia, 

 he took advantage of it to endeavor to determine the relative value of 

 these two constituents, since, when comparing this combination with 

 nitrate of lime, the former contains two equivalents of nitrogen, while 

 4 A 



