102 J. B. Gilbert — Points in connection with Vegetation. 



atmosphere. But I think I am right in saying that the con- 

 clusion of both of these experimenters is that this action takes 

 place in a very immaterial degree in natural vegetation. 



In reference to this subject, I may observe that the results 

 of the determinations of the ammonia in the atmosphere by- 

 different experimenters, and in different localities, vary very 

 greatly; and it may be concluded that a shower of rain will 

 wash out much of it. According to M. Schlosing's statement 

 of the results of his recent determinations of the ammonia in 

 the air of Paris (Compt. Eend., lxxxi, p. 1252 et seq.), it ranges 

 from one part in about 12,500,000, to one part in about 

 260,000,000 of air by weight If, for the purpose of illustra- 

 tion, we assume that, on the average, the ambient atmosphere 

 in the open country — in Europe, at any rate — will contain one 

 part of ammonia in 60,000,000 of air, or one part of nitrogen 

 as ammonia in about 50,000,000 of air, the atmosphere would 

 thus contain more than 8,000 times less nitrogen as ammonia 

 than carbon as carbonic acid. But cereal crops contain one 

 part of nitrogen to about thirty of carbon, and leguminous 

 crops, one of nitrogen to fifteen, or fewer, of carbon. On these 

 ons, the ambient atmosphere would contain a pro- 

 portion of nitrogen as ammonia, to carbon as carbonic acid, 

 about 267 times less than that of nitrogen to carbon in cereal 

 produce, and about 534 times (or more) less than that in legu- 

 minous produce. It is true that water would absorb very 

 much more nitrogen as ammonia, or dissolve very much more 

 as carbonate or bi-carbonate of ammonia, than it would of 

 cArbon as carbonic acid under equal circumstances. Hence, 

 there would appear to be a compensating quality for die small 

 actual and relative amount of nitrogen as ammonia in the 

 atmosphere, in the greater solubility or absorbability of the 

 compounds in which nitrogen exists, than of the carbonic acid 

 in which the carbon is presented. Further, it can hardly be to 

 merely a greater extent of leaf or above-ground surface that the 

 result could be attributed. Thus, though a bean and a wheat 

 crop may yield about equal amounts of dry matter per acre, 

 the bean produce would contain from two to three times more 

 nitrogen, and approximate measurements show that a wheat 

 plant offers a greater external superfices in relation to a given 

 weight of dry substance than a bean plant, and greater still 

 therefore in relation to a given amount of nitrogen fixed. If, 

 then, the bean can in some way take up more nitrogen from 

 the atmosphere than the wheat, the result must be due to 

 character and function, rather than to mere extent of surface 

 above ground. It may, however, be observed that, as a rule, 

 even those of the leguminous crops which are grown for their 

 ripened seed, maintain their green and succulent surface, over 



