1 6 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



evidence of both occurring on the same rootlet. A 

 semi-Ectotrophic may occur with an Endotrophic form 

 on the same rootlet, e.g. larch. 



4. Three distinct types of mycelium may occur in Ectotrophic 



mycorhiza : 



(a) Regular, non-vesicular, septate mycelium with clamp 

 connections. 



{b) Irregular, vesicular, non-septate mycelium with no 

 clamp connections. 



(c) Intermediate form between {a) and (b) with vesicles. 

 The types {a) and {b) may occur on the same mycorhiza. 

 These three types may represent different stages in 

 the development of the mycorhiza fungus. Type {b) 

 is probably the most intimate and forms " True " 

 mycorhiza in contrast to {a) which forms "False" 

 mycorhiza. 



5. In the Ectotrophic form the destruction of the rootlets 



by the enveloping mycelium ensues in all species in 

 all soils. 



6. No evidence of digestion of mycelium exists in the case 



of Ectotrophic mycorhiza in the Coniferae. 

 - 7. There is evidence of digestion in the case of the 

 Endotrophic forms of larch, and of Sciadopitys. 



8. The fungus invariably covers the older parts of the root- 



system in the Ectotrophic form, and the new rootlet on 

 bursting through the cortical cells carries the fungal web 

 with it, and so at no time is devoid of a fungal covering. 



9. In older parts of the roots an intracellular mycelium 



often occurs, especially in peat soils. It has none of the 



characters of a mycorhiza fungus, but it 

 {a) May produce vesicles similar to those found on 



Ectotrophic and Endotrophic forms ; 

 {b) May become thick and fleshy as in Endotrophic forms. 



II.— THE RELATION OF THE MYCORHIZA TO THE 

 FOREST TREE. 



There are two schools of opinion regarding the relation of 

 mycorhiza to the forest tree. One school is represented by 

 those who believe that the fungus in association with the roots 

 of the Higher Plant benefits the Higher Plant ; the other by 

 those who regard the fungus not only as useless but even 



