TREE ROOTS: THEIR ACTION AND DEVELOPMENT. 1 7 



harmful in its association. The evidence is confusing and the 

 relation is obscure.^ 



There is evidence that mycorhiza accompanies good growth 

 in conifers in many soils, particularly peat ; but in these cases 

 there is no evidence as to how the Ectotrophic mycorhiza in 

 such soils transfers mineral bases to the tree, or otherwise 

 benefits the tree, since there is no evidence of digestion. 

 Then again, in the case of Endotrophic forms where there 

 is evidence of digestion, there is no communication visible 

 on the part of the fungus with the soil, and it therefore 

 cannot perform the function of transferring mineral bases 

 to the plant, for it has no connection with the medium in 

 which the plant is growing. Investigators have sought to 

 show how the fungus transfers bases to the plant by some 

 process. 



Taking peat as a type of soil in which conifers tend to develop 

 mycorhiza, it may be accepted that two features in connection 

 with peat in situ are (i) deficient aeration and oxidation, and 

 (2) deficiency in mineral bases in the soil solution as contrasted 

 with most other soils. It will be shown in the course of a 

 subsequent paper that these two factors are factors influencing 

 mycorhiza development and distribution generally. In certain 

 respects these two factors are interrelated. The question arises 

 as to how plants in habitats of deficient oxygen supply, where 

 the disintegration of plant remains and the liberation of plant 

 f)od is at a minimum, succeed in obtaining mineral bases and 

 plant food. Enzyme action, particularly that class of enzymes 

 called Oxidases, suggests itself as a probable source of power 

 in this respect. Through enzyme action is it not just as 

 probable that the fungus acts on the soil medium and by its 

 action brings nutrient materials in contact with the plant roots 

 in an available form, as that the fungus first absorbs the mineral 

 bases and transfers them by some unknown process to the 

 Higher Plant? If this is so then the plant and fungus feed at a 

 common table, but the food is provided through the action of 

 the fungus, the Higher Plant absorbing the nutrient materials 

 direct. 



^ See Petri — "The present state of our knowledge of the physiological 

 significance of the mycorhiza of trees," Bull, of Agric. Intelligence and 

 Plant Diseases (International Institute of Agriculture), 1915. 



VOL. XXXVII. PART I. B 



