194 



put in them. As cold retards, and heat, up to certain limits, favors 

 the growth of bacteria, the advantage of keeping milk cold and cream 

 warm is easily explained.'' 



BULLETIN No. 5, OCTOBER, 1889. 



Atmospheric nitrogen as plant food, W. O. Atwater, Ph. D., 

 AND C. D. Woods, B. S. (pp. 1-18). — This is a condensed report of 

 an investigation in continuation of one begun some years ago by 

 Professor Atwater at Wesleyan University, where the chemical work 

 of the Station is done. Those experiments, of which results were 

 published in 1882-85, showed that leguminous plants (peas) acquired 

 large quantities of nitrogen from the air and implied that free nitro- 

 gen was probably thus assimilated. These conclusions have since 

 been confirmed by other experiments, especially those of Hellriegel, 

 who pointed out the connection of bacteria and root tubercles with 

 the gain of nitrogen. The present experiments were for a further 

 study of the acquisition of atmospheric nitrogen by different plants 

 and the relation of root tubercles thereto. Details are reserved for 

 the annual i-eport of the Station for 1889. Eighty-nine experiments, 

 divided into five series, were performed with peas, alfalfa and oats. 



The plants Avere groAvn in glass jars containing sand, purified by 

 washing and igniting. Nutritive solutions, either free from or con- 

 taining known quantities of combined nitrogen in the form of nitrate 

 of potash or lime, Avere applied to the sand. The amounts of nitrogen 

 supj^lied in nutritive solutions and seed were compared with the 

 amounts found at the end of the experiments in residual solutions 

 and i^lants. The difference between these tAvo amounts must show the 

 loss or gain in nitrogen. A gain must represent the nitrogen ac- 

 quired from the air in excess of ajiy lost either from organic matter 

 of seed or plant or from nitrate of the food. 



The results of these and similar experiments by these authors and 

 others are thus summarized : 



"(1) Peas, alfalfa, serradella, lupine, cloA'er in all probability, and 

 aj)parently leguminous plants in general, are al)le to acquire large 

 quantities of nitrogen from the air during their period of groA\^tli. 



"(2) There is scarcely room to doubt that the free nitrogen of the 

 air is thus acquired by plants. 



"(3) That there is a connection betAA'een root tubercles and this 

 acquisition of nitrogen is clearly demonstrated. Wliat this connec- 

 tion is, what are the relations of micro-organisms to the root tuber- 

 cles, and the acquisition of nitrogen, and in general how the nitrogen 

 is obtained, are questions still to be soh'ed. 



"(i) The cerealb Avith AA-hich experiments haA'e been completed 

 have not manifested this power of acquiring nitrogen, nor do they 

 have such tubercles as are formed on the roots of legumes. 



"(5) In the experiments here reported the addition of soil infu- 



