tree roots: their action and development. 15 



Analysis. 



An analysis of the previous descriptions produces the follow- 

 ing general points : — 



1. The following types of mycorhiza are present in the 



Coniferae : 

 (a) Ectotrophic — Pinus sylvestris^ Pinus montana and Pinus 



sp. in general, Picea sitchensis, Picea excelsa, Abies 



grandis, Tsuga albertiana^ Pseudotsuga Douglasii^ 



Sciadopitys verticillata. 

 (h) Endotrophic — Thuja gigantea, Sciadopitys verticillata^ 



Pinus sylvestris, 

 {c) Semi-Ectotrophic — Tsuga albertiana. 

 (d) Semi-Ectotrophic associated with an Endotrophic — 



Larix europaea. 



2. Mycorhiza involves the modification of the root-system, 



A. — Ectotrophic Forms, 



(a) In all cases there is a tendency towards the thickening 



of the rootlets, and generally in most cases a stunting 

 or shortening of the rootlet. 



(b) The mycorhiza may take the form of nodules or coral- 



like bodies, due to the repeated dichotomous branching 

 of the rootlets — Pinus sp. and Pseudotsuga Douglasii to 

 a lesser extent. 



(c) The mycorhiza may be single rootlets modified — Picea 



sitchensis, Picea excels a, Abies grandis^ Pseudotsuga 

 Douglasii, Tsuga albertiana. 



{d) Root-hairs become entirely suppressed. 



{e) There is a tendency towards compactness in the root- 

 system as a whole. 



B. — Endotrophic Forms, 



(a) The roots are thick and fleshy. 



ib) There is a great extent of fresh absorbing tissue as 

 compared with normal roots. 



(^r) There is a tendency towards compactness of the root- 

 system. 



{d) Root-hairs are absent. 



3. Both forms, Ectotrophic and Endotrophic, may occur on the 



same plant, e.g. Scots pine, but there is no conclusive 



