70 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. lxii. 



filaments take upon themselves the oiSice of roots he could 

 not doubt, for owino- to their universal distribution all over 

 the growing root system of the plant, and the entire 

 suppression of the root hairs, there was no other way in 

 which the trees could obtain soil nourishment. It would 

 thus seem that the fungus acted towards the tree the part 

 of a nurse. Its delicate filaments, ramifying through the 

 mass of organic debris, absorbed the nutritive matter found 

 there ready made, and poured it into the roots of the trees. 

 If that is a true account of what takes place in the 

 nourishment of forest trees, it must be regarded as revolu- 

 tionising our views regarding the physiology of plant 

 nutrition. If the mineral food which these trees require 

 is supplied to them by the organic sap) of the fungus, it 

 must be supplied in some form of organic combination, and 

 in that case the trees must owe, not only their mineral, 

 but also some of their organic constituents to the fungus 

 that feeds them. Before the days of Liebig, that is to say 

 during last century and a considerable part of this one, it 

 was universally believed that plants obtained their organic 

 matter from the soil, and humus was regarded as the one 

 essential of fertility. The accumulation of humus in the 

 soil was the aim the cultivator of the soil had before him ; 

 and when we consider that it was the leading principle 

 guiding the most intelligent farmers in their operations 

 for centuries, there must have been, and there must still 

 be, a good deal of permanent truth in it. 



It was Liebig's greatest achievement to fight against and 

 completely demolish this view, and cause it to be superseded 

 by what was called by him the mineral theory of plant 

 nutrition. This theory established, on the firm basis of 

 actual experiment, the fact that plants did not require to be 

 supplied with organic matter, that, on the contrary, it was 

 the great function of their life to manufacture organic 

 matter ; and perfectly unexceptional experiments were 

 carried out in which the plants of our ordinary field crops, 

 chiefly cereals, were grown both in aqueous solutions and 

 in mere sand containing no oi^ganic matter wdiatever, but 

 only solutions of certain salts containing the mineral 

 nourishment that the plants required. The organic matter 

 of plants was proved to be made in their leaves, while the 



