Chap, hi The absorption of Nitrogen 349 



economic importance led to investigations as to whether 

 it may not be more general. These researches were 

 pursued especially towards the end of our period, and are 

 still in progress. 



The observed phenomena led Frank, in 1890, to suggest 

 that free nitrogen may be appropriated from the atmosphere 

 in some such way by all plants, an opinion that has not 

 even now been disproved. True, failures to support it by 

 experiment have been more numerous than successes, but 

 it for the present remains an open question. In 1893 

 Petermann showed that barley cannot fix nitrogen in sterile 

 soil, but that an energetic fixation takes place when it is 

 grown in soil containing algae and bacteria. He made no 

 investigations, however, into these. The experiments of 

 Aeby in 1896 and of Pfeiffer and Franke in 1897 gave only 

 negative results. 



Symbioses between other plants have been found to exist, 

 and in certain cases to show appropriation of nitrogen from 

 the air. In 1896 Hiltner proved that the nodules which 

 grow upon the roots of the alder are concerned in such 

 work. When they are absent it can develop only if nitro- 

 genous compounds are supplied, but after they have been 

 formed it can thrive at the expense of atmospheric nitrogen. 

 Nobbe, Schmid, Hiltner, and Hotter described the organism 

 of Elaeagnus nodules, which they held to behave in the same 

 way. They were investigated by Nobbe in 1892 and 1894. 

 Nodules growing on the roots of Podocarpus were 

 studied by Nobbe and Hiltner. In 1899 they published 

 the outcome of five years' work upon the subject, in 

 the course of which they were able to cultivate the plant 

 in quartz sand from which nitrogen was entirely absent. 

 In the same year Hiltner investigated Lolium temulentum, 

 with which a fungoid growth was associated, and thought 

 he noted an appropriation of nitrogen. Since the close of 

 the century much investigation has been devoted to the 



