328 ASSIMILATION. 



above subject were made by Boussingault in 1837, 1 who era- 

 ployed the following method : In calcined soil, supplied with dis- 

 tilled water, and having free access of air, clover was cultivated 

 for two and for three months, and at the end of that time it was 

 found that there was a very slight gain in nitrogen over the 

 amount which had been present in the seed sown. In two 

 parallel experiments with wheat no gain was observed. One 

 year later, peas, clover, and oats were experimented on ; both 

 the peas and clover gained a little nitrogen, but there was no 

 gain whatever in the case of the oats. Boussingault's conclu- 

 sions from this series have been stated as follows : Under several 

 conditions certain plants seemed adapted to take up the nitrogen 

 in the atmosphere, but it is still a question under what circum- 

 stances and in what state the nitrogen is fixed in the plants. 



866. It was not, however, until 1851 that the subject received 

 any further attention from Boussingault. In that and the two 

 subsequent years his experiments were conducted with certain 

 precautions, by which the plants were confined in limited vol- 

 umes of air ; and in no case was an unequivocal gain in nitrogen 

 to be detected. In 1854 he placed plants in a suitable recep- 

 tacle where they could be supplied with a current of air washed 

 to free it from all traces of combined nitrogen. The atmosphere 

 within the receptacle was furnished with from two to three 

 per cent of carbonic acid. In all of the experiments, part of 

 which were upon leguminous plants, there was a slight loss of 

 nitrogen. 



867. During the progress of the experiments now alluded to 

 others were conducted in the following manner : Plants were 

 placed in a case from which nearly all dust could be excluded, 

 but which would allow of a free circulation of the external air ; 

 and under these circumstances there was the very slight gain in 

 nitrogen equal to about one twelfth of that contained iu the seed 

 sown. Boussingault attributed this almost inappreciable gain 



Priestley : Experiments and Observations on Different Kinds of Airs, iii., 

 1772. 



Sanssure : Recherches chimiques sur la vegetation, 1804, p. 205. In this 

 will be found a short account of the results of the previous observers and also 

 of Saussure's own conclusions, which are, that plants do not appropriate any 

 appreciable amount of nitrogen furnished to them as it exists in the atmosphere 

 in the free state. 



1 For a short but excellent abstract in English of Boussingault's researches, 

 referred to in the text, the student may consult Philosophical Transactions of 

 the Royal Society for 1861, p. 447. The original communications are in 

 Annales de Chimie et de Physique, ser. 2, tomes Ixvii. and Ixix., 1838. 



