282 ANNUAL OF SCIENTIFIC DISCO VERY. 



% 



question has always been answered negatively, the author remarks that it is, 

 however, known that plants do not draw all their nitrogen from the soil, 

 the crops produced every year in manured land giving a greater proportion 

 of nitrogen than is contained in the soil itself. The question which he 

 has proposed to himself for solution is, Whence, then, comes the excess of 

 nitrogen which the crops contain, and, in a more general manner, the 

 nitrogen of plants, which the soil has not furnished ? He divides his in- 

 quiry into the three following parts : 



First. Inquiry into and determination of the proportion of the am- 

 monia contained in the air of the atmosphere. 



Second. Is the nitrogen of the air absorbed by plants ? 



Third. Influence on vegetation of ammonia added to the air. 



1. The author remarks, that since the observation of M. Theodore de 

 Saussure, that the air is mixed with aramoniacal vapors, three attempts 

 have been made to determine the proportion of ammonia in the air ; a 

 million of Jkilograrnmes of the air, according to M. Grayer, contain 0.333 

 kil. ammonia; according to Mr. Kemp, 3.880 kil. ; according to M. 

 Fresenius, of the air of the day, 0.098 kil. ; and of night air, 0.169 kil. 

 He states that he has shown the cause of these discrepancies, and proved 

 that the quantity of ammonia contained in the air is 22.417 grms. for a 

 million of kilogrammes of the air, and that the quantity oscillates be- 

 tween 17.14 grms. and 29.43 grms. 



2. The author states that, though the nitrogen of the air is absorbed by 

 plants, the ammonia of the air contributes nothing to this absorption. 

 Not that ammonia is not an auxiliary of vegetation, but the air contains 

 scarcely 0.0000000224, and in this proportion its effects are* inappreciable. 

 These conclusions are founded upon a great number of experiments in 

 which the plants lived at the expense of the air, without deriving any 

 thing from the soil. For the present he confines himself to laying down 

 these two conclusions : 1. The nitrogen of the air is absorbed by plants, 

 by the cereals, as by all others. 2. The ammonia of the atmosphere per- 

 forms no appreciable part in the life of plants when vegetation takes 

 place in a limited atmosphere. After describing the apparatus by means 

 of which he carried on his experiments on the vegetation of plants placed 

 in a soil deprived of organic matter, and the manner in which the experi- 

 ments were conducted, he adduces the results of these experiments in 

 proof of the above conclusions. 



3. With reference to the influence of ammonia on vegetation, the au- 

 thor states that, if ammonia be added to the air, vegetation becomes 

 remarkably active. In the proportion of four ten- thousandths, the influ- 

 ence of this gas shows itself at the end of eight or ten days, and from this 

 time it manifests itself with continually increasing intensity. The leaves, 

 which at first were of a pale-green, assume a deeper and deeper tint, and 

 for a time become almost black ; their petals are long and upright, and 

 their surface wide and shining. In short, when vegetation has arrived at 

 its proper period, the crop is found far beyond that of the same plants 



