6 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



2. Tree-Roots : Their Action and Development. 



{With Plates.) 

 By Ernest V. Laing, Royal Botanic Garden, Edinburgh. 



It is proposed that the following notes should be the first of 

 a series dealing with tree-roots, their action and development, 

 more especially in peat soils, with a view to throwing some 

 light on the factor or factors, causing or contributing to the 

 inhibition from many peat soils of coniferous trees. The notes 

 are the result of research carried out at the Royal Botanic 

 Garden, Edinburgh, under Professor W. Wright Smith. 



Coniferous tree-roots are of two main types: — (i) Normal 

 roots bearing root-hairs, and (2) mycorhiza-bearing roots. Since 

 all good growing trees in peat (with the possible exception of 

 spruce, which, under certain conditions to be dealt with in a 

 subsequent paper, produces root-hairs) are mycorhiza trees, it 

 is with the latter that the present paper will deal. 



In the first place, it is proposed to give certain observations 

 on the structure of the mycorhiza of the Coniferae ; and in the 

 second, to describe an enzyme production which may serve in 

 some measure to explain the beneficial action of mycorhiza on 

 tree-growth, namely, the secretion by mycorhiza of Oxidases. 



I.— THE MYCORHIZA OF THE CONIFERAE. 



Mycorhiza, or the intimate union of a fungus with the roots 

 of a Higher Plant, generally accepted as a case of symbiosis, 

 may take one of two forms. The fungus may form a web of 

 mycelium to the outside of the root, in which case it is spoken 

 of as Ectotrophic mycorhiza; or the fungus may be contained 

 exclusively within the cells of the cortex, in which case it is 

 called Endotrophic mycorhiza. These two types, however, are 

 connected by mtermediate forms. Both Ectotrophic and Endo- 

 tiophic mycorhiza occur within the Coniferae. The Ectotrophic 

 torm was first demonstrated and described by Frank, and 

 Tubeuf pointed out that the Endotrophic form was often 

 characteristically developed in trees. 



In order to obtain an idea as to the form and condition 

 of the mycorhiza of the Coniferae, the following have been 



