204 MASSACHUSETTS HORTICULTURAL SOCIETY. 



ducts of vegetable growth ; this may take place, possibly, in the 

 very tissues of the plant itself. 



Fifth. lu ordinary arable soils, wherever the air penetrates 

 them — and the more abundantly the freer the access of air, other 

 conditions being favorable — by the help of a certain class of the 

 living organisms called bacteria. 



In some of Boussingault's earlier experiments, in all of his later 

 ones, and in all of the experiments of Lawes, Gilbert, and Pugh, 

 the plants were excluded from all of these sources of supply ; 

 these experiments simply proved that plants can make no use of 

 the free nitrogen of the atmosphere through any power possessed 

 by them of working it up into compounds containing nitrogen. 

 Ville pretended to exclude his plants in his iron-framed glazed 

 case from all these sources of nitrogen, also ; but as they were 

 somehow supplied with nitrogen compounds not mentioned in his 

 account of his work, his experiments prove nothing. 



Prof. Atwater's experimental plants were excluded from the 

 first source of supply- only, the ammonia and nitrate brought down 

 by the rain ; they had the full benefit of all the other sources, so 

 far as free exposure to the air is concerned ; but the soil that he 

 used was simply sand charged with known quantities of plant food. 

 As sand has little power of absorbing gases, he himself does 

 not think that much nitrogen would become serviceable in that 

 way ; and as Berthelot's results, where the assistance of the 

 bacteria came in, were obtained with soils containing clay, it re- 

 mains yet to be determined whether these bacteria will do the 

 same work in a sand. Finding little else to stand upon, in ex- 

 planation of his results, Prof. Atwater refers them, at least in part, 

 to the electrical action above mentioned ; but further investiga- 

 tions must show whether so large gains could be made in this way 

 alone. It seems to me very doubtful, and, for my own part, I must 

 consider his results as not yet satisfactorily explained. 



There is, I think, good and sullicient evidence, in this summing 

 up of the several modes in which the crops may derive nitrogenous 

 food from the atmosphere, and in my statement of the facts on 

 which that summing up is based, — 



First. That nitrogenous food can be obtained from that source, 

 directly or indirectly, in considerable quantity, under favorable 

 conditions. 



And, Second, lliaL there are possibilities of supply by some of 



