Lecture IX — 131 — Structure 



infection; while in all ericads studied the youngest roots had some 

 portions fungus-free. 



The Pyrolas studied by Furth (1920) had the mycelium spread 

 over the whole length of the root but confined to the epidermal cells 

 which were hypertrophied and gradually filled completely with hyphae 

 that cause the death of the cell and result in development of "clumps". 



Goralloid Mycorrhizae: — The various pine mycorrhizae are 

 described with difficulty, largely because there is so little information 

 available about them. Although so many papers have been published 

 on pine, there are very few anatomical studies about them extant. 

 That is especially true of recent times, for the trend at present is 

 toward philosophical disquisitions on the nature of mycotrophy, a 

 branch of learning that conveniently eliminates the drudgery of sec- 

 tioning. Hence knowledge of pine mycorrhizal anatomy is largely 

 confined to two European species, — P. montana and P. sylvestris; 

 and there is almost nothing on American pines. But coralloid mycor- 

 rhizae are not confined to pines since they occur on other plants, — 

 on how many others no one could say. 



Knowledge of coralloid mycorrhizae (Gabelmykorrhizen) dates 

 back at least to Reess (1887) although they are said to have been 

 first described by Hartig in 1851. Moller (1902) said that they 

 were well known in P. sylvestris while in 1908 he recorded 

 them from sand of the Brandenburg Marches but absent from humus. 

 Infection in P. sylvestris and Picea Abies (Melin, 1921) is through 

 root hair or epidermal cell and hyphae grow at first intracellularly 

 in outer cortical cells where they form a pseudoparenchyma, but later 

 form an Hartig net and mantle. Similarly, Abies firma mycorrhizae 

 (Masui, 1 926^7 ) have not only a mantle and Hartig net but intra- 

 cellular infection. In Larix the fungus penetrates intracellularly into 

 the roots (Melin, 1923) and forms individual hyphae or knots which 

 in time are digested, after which the fungus penetrates intercellularly 

 and the mycorrhiza becomes more strictly ectotrophic. 



In synthesis experiments with pine (Melin, 1923), only ectendo- 

 trophic mycorrhizae were obtained. 



Tuberous Mycorrhizae: — "Knollenmykorrhizen" were brought 

 into the limelight by Muller (1902) who regarded them as similar 

 to the coral clusters of cycads and some legumes. They are formed 

 by a dichotomy which is rare amongst roots, yet not called forth here 

 by a fungus: "We stress the fact that the dichotomous branched 

 tubercle is not invaded until after its dichotomy has been manifested". 

 Both racemosely and dichotomously branched mycorrhizae occur 



