137 



life and yield a crop comparable with that obtained with a eood sup- 

 ply of nitrate. The amount of nitro<»en in the crop is sometimes a 

 very large gain over that contained in the soil ; this latter also occurs 

 when the air is deprived of all ammonia, etc., and the nitrogen must be 

 obtained from the free nitrogen of the atmosphere. But when the 

 soil is sterilized by heat and the pots and seeds are sterilized as to 

 their surfaces by washing with very dilute mercuric chloride, then peas 

 behave like oats and barley; there is no gain of nitrogen from the air, 

 the crops are proportional to the quantity of nitrate in the soil, and 

 no tubercles are formed on the roots. 



In all cases where the peas had gained nitrogen when planted in 

 unsterilized soil, tubercles are formed on the roots, and, on the other 

 hand, when they are planted in sterilized soil no tubercles are formed 

 unless we add to the soil the washings of a small quantity of arable 

 soil, in which case tubercles are generally formed. Such washings 

 may themselves be sterilized by boiling or possibly by lower tempera- 

 tures. 



The authors infer that the assimilation of. nitrogen from the air 

 by peas, lupines, and other leguminous plants is not within the power 

 of the plant as such; nor can it take place when the plant grows 

 within a sterilized medium, but is connected with the presence of mi- 

 crobes and with the development of tubercles on the roots. (Agr. 

 Sci., Vol. Ill, p. 215.) 



The fixation of nitrogen by Leguminosao has been studied b}' E. 

 Breal, who succeeded in inoculating Spanish beans with bacteria from 

 tubercles on the roots of Cystisa. At first the growth was vigorous, 

 then the plant languished, but eventually recovered, flourished, and 

 matured. Again, lucerne, growing in a pot in sandy soil, was inocu- 

 lated by laying a fragment of tuberculous root of lucerne on the soil 

 and watering the plant with drainage water. In both these cases not 

 only did the plants gain in nitrogen, but the soils also, so that this 

 experiment confirms the ordinary experience as to the behavior of 

 the Leguminosa^ as soil improvers. (Agr. Sci., Vol. IV, p. 75).) 



Lawes and Gilbert, in a memoir published in the Philosophical 

 Transactions of the Royal Society of London for 1889, state their 

 conclusions as to the sources of the nitrogen in the plant as follows: 



In our earlier papers we had concluded that, excepting the small 

 amount of combined nitrogen coming down in rain and the minor 

 aqueous deposits from the atmosphere, the nitrogen source of crops 

 was the stores within the soil and subsoil, whether from previous 

 accumulations or from recent manuring. * * * With the Grami- 

 neae it was concluded that most, if not all, of their nitrogen was 

 taken up as nitric acid. In leguminous crops, in some cases, the whole 

 is taken up as nitric acid, but in other cases the source seemed to be 

 inadequate. * * * It is admitted that existing evidence is insuf- 

 ficient to explain the source of all the nitrogen of the Leguminosa?. 



