138 



Frank had observed that the feeding roots of certain trees were 

 covered with a fungus, the threads of which forced themselves be- 

 tween the epidermal cells into the root itself, which in such cases had 

 no hairs, but similar bodies were found external to the fungus mantle, 

 which prolonged into threads among the particles of soil. Frank 

 concluded that the cldorophyllous tree acquires its nutriment from 

 the soil through the agency of the fungus. Such a mode of accumu- 

 lation by these green-leaved plants plainly allies them very closely 

 to fungi themselves: but inasmuch as in the cases observed by Frank 

 the action of the fungi was most marked in the surface layers of soil 

 rich in humus, and since this development has not been observed on 

 the roots of any herbaceous j^lants, therefore the facts hitherto 

 recorded do not aid us in explaining how the deep and strong rooted 

 Leguminosjp acquire nitrogen from the raw clay subsoils of Roth- 

 amsted. 



In continuation of their investigations, Lawes and Gilbert have 

 published a subsequent paper stating that in 1888 they began experi- 

 ments in the same line as those of Hellriegel. Peas, red clover, 

 vetches, blue and yellow lupins, and lucerne were sown in pots, of 

 which there were four to each series. No. 1 contained sterilized 

 coarse white sand; Xos. '2 and 3 contained the same sand, to which 

 a soil extract was added; Xo. 4 contained garden soil or special 

 lupin soil. Their general results were that the fixation of free nitro- 

 gen only occurred under the influence of microbes in the soils that 

 had been seeded with soil organisms by adding soil extract to the 

 sand in the pots. They find that the Rothamsted experiments indi- 

 cate that with a soil that is rich in nitrates there are far fewer nodules 

 on the roots of the plants than were formed in the pots of sand con- 

 taining but little nitrates but seeded with soil organisms. The 

 authors suggest (1) that somehow or other the plant is enabled under 

 the condition of symbiotic life to fix free nitrogen of the atmosphere 

 by its leaves, a supposition in favor of which there seems to be no 

 evidence whatever; (2) that the parasite microbe utilizes and fixes 

 free nitrogen and that the nitrogenous compounds formed by it are 

 then taken up by the plant host. On this latter supposition the 

 large gain of nitrogen, as made by the leguminous plant, when grow- 

 ing in a soil that is free from nitrogen but properh^ infected by 

 microbes, becomes intelligible. (Agr. Sci., Vol. IV, p. 201.) 



As to the relations between plants and atmospheric ammonia, almost 

 all agree that the plant derives ammonia from the atmosphere through 

 the medium of the soil only. Berthelot finds that vegetable soils 

 usually have sufficient ammonia to enable them to evolve it into tlie 

 atmosphere, but under certain conditions they can absorb this gas 

 from the atmosphere. (Agr. Sci., Vol. IV, p. 295.) 



