November 15, 1889.J 



SCIENCE. 



329 



into the following series : 1888, Champion of England peas, 25 

 trials; 1888-89, alfalfa, 5; 1889, East Hartford Early peas, first 

 series, 33 ; 1889, Champion of England peas, 16; 1889, oats, 10. 

 Other series with other plants are begun, but are not yet ready to 

 be reported upon. The following questions were proposed for 

 study: l. May plants grown under normal conditions acquire any 

 considerable amount of nitrogen, free or combined, from the sur- 

 rounding atmosphere ? 2. What effect has the addition of soil- 

 infusions upon the formation of root-tubercles? 3. Is there a 

 definite relation between the formation of root-tubercles and the 

 acquisition of atmospheric nitrogen ? 



The method was essentially the same as in the previous experi- 

 ments by Mr. Wood above described. The plants were grown in 

 glass jars containing sand, purified by washing and igniting. 

 Nutritive solutions, either free from or containing known quanti- 

 ties of combined nitrogen in the form of nitrate of potash or lime, 

 were applied to the sand. The amounts of nitrogen supplied in 

 nutritive solutions and seed were compared with the amounts 

 found at the end of the e.xperiments in residual solutions and plants. 

 The difference between these two amounts must show the loss or 

 gain ifi nitrogen. A loss nriust indicate decomposition of either the 

 organic nitrogen of the seed or plants or the nitric acid of the ni- 

 trates fed, or both. A gain must represent the nitrogen acquired 

 from the air in excess of any lost either from organic matter of 

 seed or plant or from nitrate of the food. 



The conditions of growth were varied by varying the amounts of 

 nitrogen supplied in nutritive solutions. The minerals needed for 

 the growth of the plants were added in amounts to make one 

 part or less by weight of dissolved salts in one thousand parts of 

 the solution. Some of the plants received no combined nitrogen 

 except that in the seed ; to others nitrates were added, but in 

 such small quantities that the minerals were relatively in excess ; 

 to others enough nitrogen was added to make the mixture of 

 plant-food correspond more nearly to the composition of the plants. 

 The answer to the question, " May plants grown under normal 

 conditions acquire any considerable amount of nitrogen from the 

 atmosphere ? " coincides with the earlier experiments at Mansfield, 

 and is plain and unmistakable. Peas of small, early variety (Early 

 Hartford) planted in sand, with no nitrogenous food except that in 

 the seed, grew to a height of over five feet. With nitrogen sup- 

 plied in the solutions, they sometimes reached a height of over 

 eight feet. Many of the peas and alfalfa plants accumulated large 

 quantities of nitrogen from the air. In one case a single plant 

 thus obtained more than one-third of a gram (54.6 grains) of nitro- 

 gen. 



In a number of experiments with peas in which the roots had 

 few or no tubercles, instead of gain, there was a decided loss of 

 nitrogen. This gives added force to the suggestion that if nitrogen 

 escaped in some of the trials, it may have escaped to some extent 

 in other cases also. If so, the results are all inaccurate as indica- 

 tions of the actual atmospheric nitrogen acquired, and the plants 

 must have really obtained more than the figures imply. 



It may be that the loss of nitrogen is greater in some classes 

 of plants than in others. The apparent loss in the experiments 

 with peas was about as large when they were not fed combined 

 nitrogen, other than that in the seed, as when they were fed con- 

 siderable quantities of nitrates. In the experiment with oats the 

 results were very different. Without the addition of nitrates, there 

 was no loss, but a slight gain. When nitrates were fed, there was 

 loss ; and the larger the amount of nitrates added, the greater was 

 the loss of nitrogen. 



These experiments do not tell to what extent the loss observed 

 with the oats, and with the peas which had no root-tubercles, was 

 from the seed, and to what extent from the nitrates ; whether, as 

 seems most likely, it was due to the action of microbes ; or what 

 connection there may be between plants of different species and 

 the loss of nitrogen. These and kindred questions must remain 

 for future research to decide. But one can hardly help coupling 

 this observation of the large loss of nitrogen in the oat experiments 

 with the common observation of practical farmers that oats are an 

 exhaustive crop. The power of leguminous plants to acquire ni- 

 trogen from the air evidently explains in part why they are such 

 valuable " renovating crops." 



Experiments by Berthelot and others imply that nitrogen is be- 

 ing continually gathered from the air by soils, and that microbes, 

 and probably electricity, aid the process. A large amount of late 

 research tends to show that nitrogen compounds in the soil are be- 

 ing constantly decomposed by the action of microbes, and that the 

 nitrogen thus set free escapes into the air. 



In Hellriegel's experiments the development of the root-tuber- 

 cles on the plants seemed to be dependent upon the addition of 

 soil-infusions : in those of the Storrs School Station, although the 

 sand 'and water were sterilized, root-tubercles were often abun- 

 dant where no soil-infusions were added. This was especially the 

 case where the plants had some nitrogenous food. Indeed, where 

 the plants were reasonably well fed, so far as the root-tubercles 

 were concerned, it made no apparent difference whether they had 

 soil-infusions or not; nor was there much difference where the 

 plants had no nitrogen in their food. The plants were grown near 

 a garden in which the soil was rich ; and the microbes, which seem 

 to be connected with the root-tubercles, were probably abundant. 

 The most natural explanation is, that the organisms or their germs 

 (spores) were floating in the air ; found their way to the pots in 

 which the plants were cultivated, and grew there ; and that the 

 growth of the microbes was especially favored where the plants 

 had nitrates, i.e., had food enough to keep them vigorous until the 

 tubercles were formed. 



These experiments, like those of Hellriegel, reveal a remarkable 

 relation between root-tubercles and the acquisition of nitrogen 

 from the air by plants. Leguminous plants thus far experimented 

 with have root-tubercles, and acquire atmospheric nitrogen. Other 

 plants have been found to be without root-tubercles, and to gain 

 little or no nitrogen ; while in some experiments, as in those with 

 oats, above cited, there is a large loss. There is an evident con- 

 nection between root-tubsrcles and microbes, though the exact 

 nature of the microbes and their connection with the tubercles re- 

 main to be explained. 



While there is as yet no positive proof that the root-tubercles 

 or the microbes are the cause of the gain of nitrogen, the fact that 

 there is a connection between the root-tubercles and the amount 

 of nitrogen acquired by the plants from the air is unmistakable. 

 In every case, without exception, where there were no root-tuber- 

 cles, there was loss of nitrogen ; where there were " few " tuber- 

 cles, there was sometimes a slight loss ofjnitrogen, at other times 

 a slight gain ; with a " fair number " of tubercles, there was a de- 

 cided gain ; where there was a " large number " of tubercles, the 

 gain of nitrogen was very large. 



It may be that this relation holds in fields as well as in pot-cul- 

 ture. The past season the station grew a half-acre of cow-peas, 

 which yielded at the rate of about eight tons of green fodder 

 per acre. In some ten different places in the field the roots 

 were examined, and found to be covered with tubercles of large 

 size. At one end of the field, where the yield was relatively light, 

 the roots had less tubercles than elsewhere, and in general where 

 the growth was heaviest the tubercles seemed to be most abun- 

 dant. 



As to whether the nitrogen which the plants obtain is the free 

 or the combined nitrogen of the air, these experiments do not 

 bring absolute proof, but the quantities of nitrogen obtained are so 

 very large as to leave little doubt that it is free nitrogen ; and the 

 experiments of Hellriegel above cited would seem to prove that 

 the uncombined nitrogen can thus be used. This and the cog- 

 nate question as to how the nitrogen is acquired, demand further 

 study. Investigations in this line are being planned for at the 

 station. 



This subject has a wider significance than what has been said 

 above implies. The future welfare of our race, material, intel- 

 lectual, and moral, depends upon the food-supply, or, in other 

 words, upon the product of the soil. This, in turn, reduces itself 

 essentially to a question of phosphoric acid, potash, and nitrogen. 

 Enough of the first two for indefinite time to come is assured in 

 the deposits of phosphates and potash salts already discovered, but 

 the probability of a sufficient supply of nitrogen has been ques- 

 tioned. This costliest of the fertilizing elements escapes from our 

 soils into the air and into the sea, and is taken away by crops, and 

 not completely returned. Artificial fertilizers promise to meet but 



