114 



Sir J. B. Lawes and Prof. J. H. Gilbert. 



sidered. He observed that the feeding roots of certain trees were 

 covered with a f ungus, the threads of which forced themselves between 

 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. In the case 

 of the Cupuliferae the occurrence seemed to be universal, and it was 

 to a great extent limited to them, though it has been observed on 

 willows, and on some conifers. The development was the greatest in 

 the first few inches or richer layers of soil. Frank considered the 

 action to be one of true symbiosis, and concluded that the chlorophyl- 

 lous tree acquires its soil nutriment through the agency of the 

 fungus. 



Here, then, is a mode of accumulation by some green-leaved plants 

 which allies them very closely to fungi themselves ; indeed, it is by 

 an action on the soil which characterises non-chlorophyllous plants, 

 that the chlorophyllous plant acquires its soil supplies of nutriment. 

 But inasmuch as the action is the most marked in the surface layers 

 of soil rich in humus, and it is stated that the development has not 

 been observed on the roots of any herbaceous plants, the facts so far 

 recorded do not aid us in the explanation of the acquirement of 

 nitrogen by deep and strong rooted Leguminosae from raw clay sub- 

 soils. Still, in view of the office within the soil which is by some 

 attributed to micro-organisms, and other low forms, the observations 

 are not without interest. 



Only very brief reference can be here made to the numerous experi- 

 ments which have been conducted in recent years, the results of which 

 are held to afford evidence that free nitrogen contributes to the yield 

 in our crops — either through the agency of the plant itself, or of the 

 soil under the influence of micro-orga-nisms, or of other non-chloro- 

 phyllous forms. 



Some years ago, Berthelot called in question the validity of the con- 

 clusions from the experiments of Boussingault, ourselves, and others, 

 in which it was sought to determine whether plants assimilated the 

 free nitrogen of the atmosphere, by growing them in enclosed vessels 

 which excluded the possibility of electrical action within the plant or 

 the soil. It is at any rate coincident with the pretty general acceptance 

 of this objection, which obviously puts out of court more exact 

 methods, and exposes the experimenter to many more possible sources 

 of error, that there has been a great accession of experimental evi- 

 dence adduced, which is held to show the participation of the free 

 nitrogen of the atmosphere in the results of growth. Had the results 

 so obtained by various experimenters been at all accordant one with 

 another, the fact might have been considered proof that the objection 

 was fully justified. They are, however, in a quantitative point of 

 view, so conflicting, without any adequate explanation in the methods 



