ON THE GROWTH OF LEGUMINOUS CROPS. 43 



we should obviously be again met with the difficulties in the way of 

 assuming that the conditions within the sub-soil would be adequate 

 for so much nitrification. 



It will be seen, therefore, that although significant indications have 

 been obtained, both as to the importance of nitric acid as a source of 

 the nitrogen of the Leguminosse, and as to the action of acids in 

 rendering soluble the otherwise insoluble nitrogenous compounds of 

 soils and sub-soils, yet on neither of these points is the evidence at 

 present available, adequate to account satisfactorily for the facts of 

 growth. 



It will be of interest, briefly to refer to some evidence relating to 

 another mode in which green-leaved plants may acquire nitrogen from 

 the stores already existing in the combined state, but in an insoluble 

 condition, in the soil and sub-soil. 



Thus, Professor Frank has observed that the feeding roots of 

 certain trees are covered with a fungus, the threads of which force 

 themselves between the epidermal cells into the root itself, investing 

 the cell, but not penetrating the nbro-vascular tissue. In such cases 

 the root itself has no hairs ; but there are similar bodies external to 

 the fungus-mantle, which are prolonged into threads among the particles 

 of soil. The fungus-mantle dies off on the older portions of the root, 

 and its extension is confined to the younger parts, those which are 

 active in the acquirement of nutriment. 



Frank considers that the conditions are those of true symbiosis; 

 and that the chlorophyllous tree acquires the carbon, and the fungus 

 the water and the mineral matters, that is the soil-nutriment. He did 

 not refer to nitrogen, but there seems no reason to suppose that the 

 fungus could not, as do the fungi in the case of fairy rings for example, 

 avail itself of the organic nitrogen of the soil. 



Here, then, is a mode of accumulation of soil-nutriment by some 

 green leaved plants, which so far allies them very closely to fungi 

 themselves. Indeed, it is by an action on the soil which characterises 

 /20ft-chlorophyllous plants, and by virtue of which they are enabled to 

 take up nutriment not available to most green-leaved plants, that the 

 chlorophyllous plant itself acquires its soil supplies of nutriment. It 

 can readily be supposed that, under such circumstances, the tree may 

 acquire not only water and mineral matter, but both organic carbon, 

 and organic nitrogen, from the soil. In reference to this point it may 

 be stated that, from the evidence so far at command, it was concluded 

 that the action is the most marked in the surface layers of the soil rich 

 in humus. 



So far as this is the case, it is obvious that such an action of fungi 

 on the soil does not aid us in the explanation of the acquirement of 

 nitrogen from raw clay sub-soil, by the deep and strong rooted 

 Legnminosse. 



Further, it is distinctly stated, that the fungus development in 

 question has not been observed on the roots of any herbaceous plants. 

 "It is, nevertheless, a point of interest, should it be established, that by 



