156 



THE ROTHAMSTED EXPERIMENTS. 



A 'point 

 still un- 

 settled. 



Peter- 



mann's 



trials. 



Barley not 

 able to fix 

 free nitro- 



Lower 

 vegetation 

 and the -fix- 

 ing of free 

 nitrogen. 



the fixation of free nitrogen under the influence of the sym- 

 biotic growth of their root-nodule-microbes and the higher 

 plant ; that there is also fixation to some extent, but quanti- 

 tatively of much less importance, by microbes within the soil ; 

 and that there is fixation to some, but to a comparatively 

 immaterial amount, by lower vegetation — such as Fungi, 

 Lichens, and some Algse. Further, it is established that 

 there is gain from free nitrogen in the case of some non- 

 leguminous higher chlorophyllous plants — Eleagnus, for 

 example — but as in the case of the Leguminosse, with the 

 coincidence of root-nodule-microbe development. There still 

 remains the question — "Whether there is any fixation by the 

 higher chlorophyllous plants themselves, independently of 

 the associated growth of lower organisms ? Frank maintains 

 that there is such fixation by various non- leguminous plants. 



In 1892, A. Petermann published the results of experiments 

 with barley in which he found gain of nitrogen, which he 

 attributed to fixation by the plant. He at the same time 

 observed that the surface of the soil was partially covered 

 with Algse. In 1893, he published the results of further 

 experiments, in which he grew barley both with and without 

 sterilisation. He found no gain with sterilisation, and attri- 

 buted that shown without it to the lower vegetation with 

 which the surface of the sand was more or less covered. He 

 concluded that barley is not able to fix free nitrogen ; but 

 that soils covered with lower vegetation become richer in 

 nitrogen. He considered that the gain in his earlier experi- 

 ments was not due, as he then supposed, to fixation by the 

 barley itself, but was brought about by the Algse growing 

 on the surface of the sand. His conclusion was that free 

 nitrogen is not fixed either by the higher plants, or by soil 

 free from lower vegetation. Liebscher, from the results of 

 an elaborate series of experiments with various plants, includ- 

 ing white and black mustard, concluded that these cruciferous 

 plants have the power of fixing the free nitrogen of the air, 

 but whether with or without the co-operation of soil-organ- 

 isms, he considered was not proved. Lotsy, on the other hand, 

 from the results of experiments with the same plants, con- 

 cludes that there is no such fixation with sterilisation, and 

 that it is uncertain whether it takes place under unsterilised 

 conditions. The question is one of practical as well as scien- 

 tific interest, as these plants are among those grown for green 

 manuring. 



Liebscher's experiments certainly appear to have been 

 conducted with very great care under the conditions selected. 

 Nevertheless, it is difficult to accept so important a con- 

 clusion from the results of experiments in which from about 



