Sources of Nitrogen in Plants . 349 
Before giving his own results Frank summarises those 
obtained by some other observers. 
Dietzell 1 found with peas and clover that there was a loss 
in nitrogen during the progress of experiments similar in 
principle to these. 
Berthelot 2 found that the soil itself can fix free nitrogen in 
combination, and that the process may depend on the activity 
of micro-organisms. The increase was not in the form of 
ammonia or nitrates, but as organic compounds. Sterilisation 
destroyed this power on the part of the soil. 
Joulie 3 found similar results. He cultivated plants in pots, 
and the nitrogen increased. 
Frank’s results are shortly as follows. In the soil with 
no plants there was a gradual loss of nitrogen ; in those 
in which the plants grew there was an increase in many 
cases. Frank concludes that ‘ the increment of nitrogen here 
observed can only be looked upon as a fixation of uncom- 
bined atmospheric nitrogen, unless we assume that this large 
quantity of ammonia has been seized from the air by the 
plant.’ 
Frank further concludes that two processes occur side by 
side in the soil — one which results in the freeing of nitrogen 
from its combinations in the soil, and another which consists 
in the fixation of nitrogen from the air — c the latter is favoured 
by the presence of living plants.’ 
Some experiments made by Dr. Vines in 1887, and com- 
municated to the British Association at Manchester, also bear 
on this subject. Dr. Vines cultivated beans in a medium 
devoid of nitrogen, and found that they went on growing 
much as if nitrogenous food-materials were present at the 
roots. 
The following paper is quoted simply to give an example 
of publications bearing on another aspect of the same question. 
In 1873 M. Deherain published a paper in the Annates des 
1 Sitzung der Section fur landw. Versuchsw. d. Naturf. zu Magdeburg, 1884. 
2 Compt. Rendus, 1885, p. 775. 
3 Ibid. p. 1010. 
B b 2 
