188 ORIGIN OF ORGANIC MATTER 



estimate of 5,263,623,000,000,000,000 kilogrammes as the weight 

 of the atmosphere, and if it contained in all regions equal quanti- 

 ties of ammonia, the amount of the latter would be 2,646,404 

 kilogrammes. Horsford* found a much larger amount of ammonia 

 than this in the atmospheric air; the greatest quantity was 

 observed in July, when there were 47' 63 parts in one million parts 

 (by weight) of air; the smallest quantity noted was in December, 

 when there were only 1*2171 parts. It would appear from the 

 observations of Horsford, that the quantity of ammonia in the 

 atmosphere is at its maximum in the summer months, when the 

 sources of ammonia are most abundant, and when it is not so 

 frequently carried off by rain and snow as in winter, and it would 

 seem to diminish in an almost constant ratio towards the winter. 



Liebig calculates that if 1 Ib. of rain water contain only half a 

 grain of ammonia, an area of 2,500 square metres will receive 

 in the course of the year with the rain (which amounts to 

 2,500,000 Ibs.) nearly 80 Ibs. of ammonia, or 65 Ibs. of pure 

 nitrogen. This would be far more than is contained in the form 

 of glutin and albumen in 2,650 Ibs. of wood, or 2,800 Ibs. of ha} T , 

 or 200 cwt. of beet-root (this being the respective produce of an 

 acre of wood, of meadow, and cultivated land). 



Several nitrogenous substances which we constantly meet with 

 in almost all plants, and more especially in their seeds, contain a 

 certain amount of sulphur, and in addition to these there are the 

 highly sulphurous ethereal oils, which may be extracted by distil- 

 lation with water from several species of the Crucifers. As the 

 air, rain, and ordinary spring-water, contain nothing beyond the 

 merest traces of sulphuretted hydrogen, plants must obtain the 

 necessary amount of sulphur from contact with alkaline sulphates, 

 and especially the sulphate of ammonia. The sulphuric acid 

 is then probably reduced by the same processes by which the 

 deoxidation of the carbonic acid is effected. It is therefore obvious 

 that the roots of plants are the organs through which sulphur is 

 absorbed. 



Having briefly considered the nature of vegetable nutrient 

 matters, and traced their various sources in inorganic nature, we 

 have next to direct our attention to the mode in which this 

 inorganic material is elaborated into organic matter in plants. 

 We should, however, most assuredly arrive at very incorrect con- 

 clusions, were we to attempt to explain the formation of organic 

 matter in plants without at the same time taking into considera- 

 * Ann. d. Ch. u. Pharm. Bd. 74, p. 243. 



