IRREGULAR NUTRITION 



195 



In these respects Fungi are better equipped than ordinary green 

 Plants, and it is this which makes a coalition with them a physiological 

 advantage. Mycorhiza may 

 even lead indirectly to a state 

 of saprophytic nutrition. 



Two different types of this 

 coalition are recognised. In 

 the first the fungus lives out- 

 side the tissues of the plant 

 with which it is related ; this is 

 described as ectotrophic, and it 

 occurs in the Beech, Horn- 

 beam, Oak, and Scots Pine; 

 also in Monotropa, and Sar codes 

 (Fig. 147). In the second the 

 fungus penetrates the tissues, 

 and it is accordingly styled 

 endotrophic ; it occurs in the 

 Heaths and Orchids, and in 

 the Club-Mosses and Adder's- 

 tongues. 



(a) ECTOTROPHIC MYCORHIZA. 



Externally roots showing 

 ectotrophic mycorhiza appear 

 wrapped round by a covering 

 of fungal origin, and are short 

 and thick, and repeatedly 

 branched. The branching is 

 sometimes endogenous as in 

 ordinary roots; but in other 

 cases it is of external origin, 

 with transition to forking in 

 the Scots Pine. Sections show 

 that .the roots are covered by 

 a thick felt of matted fungal 

 threads, which sometimes stop 



Short Of the tip (Monotropa), Whole plant of Sa^L^showing the mycorhizic 



hnf iKsiiolKr r>r>t7-^r 1'f m root-system, from which arises a bulky flesh-coloured 



USUaJlV COVer it COm- s i loot) with broad sheathing scales below, and a ter- 



pletely (Pinus, Fagus, Carpinus, ^ With prominent bracts " Reduced ' 



