Kelley — 172 — Mycotrophy 



have been overlooked, then there is nO' such thing as a true ectotrophic 

 mycorrhiza with the mycehum closely surrounding the rootlet but 

 not penetrating its cells. Were such a mantled root to exist as in- 

 dicated, then mycotrophy in such a case would inevitably consist in a 

 provision of the higher plant with materials taken directly from the 

 soil (since the higher plant is otherwise isolated from the soil by 

 felted hyphae) while the fungus would gain nothing except a con- 

 genial site for mantling its hyphae. But if the "ectotrophic" mycor- 

 rhiza actually has hyphae extending into the host-plant's cells, then 

 its mycotrophism is the same as for other sorts of mycorrhizae, 

 namely a mycotrophic phagocytosis. In the absence of definite in- 

 formation our judgment must remain suspended ; yet we can make 

 one incidental observation, that free-hand sections are useless for my- 

 corrhizal study and researches based on this method are necessarily 

 invalidated. 



If we distinguish a mycorrhiza as "ectotrophic" when it possesses 

 an Hartig net and ignore the question of infection or non-infection, 

 then the cases described by Melin as ectendotrophic may be utilized 

 for this category. In Larix (Melin, 1922&), three phases of mycor- 

 rhizal formation are distinguished: {!) The fungus penetrates in- 

 tracellularly into the roots and forms individual hyphae or knots; 

 (2) then the intracellular hyphae are digested and the mycelium pene- 

 trates intercellularly, while {3) finally the fungus lives almost ex- 

 clusively externally and the mycorrhiza becomes mainly "ectotrophic". 

 In Pinus sylvestris and Picea Abies (Melin 1922a) the hyphae grow 

 principally in the interior of the cortical cells where they form a 

 pseudoparenchyma of the same appearance as in the fungal mantle of 

 the completely developed mycorrhiza. Later the Hartig net and the 

 fungal mantle are formed. 



In Betula and Populus, Melin (1923) described the mycorrhiza 

 as consisting of (i) an hyphal mantle; (2) a "palisade" layer in 

 which there is an Hartig net and intracellular hyphae of two sorts : 

 (a) Haustorial hyphae which are very thin (1 /*) and grow in a 

 tortuous course: they are seldom septate, are plasm-poor and some- 

 times fragment while at other times they form grape-like bodies. 

 {h) Protein (Eiweiss) hyphae may attain 10 /u, thickness. They 

 extend longitudinally in the palisade cells and grow into neighbouring 

 digestion cells or penetrate several palisade cells. They are at first 

 very rich in plasm and protein and contain several (up to 8) large 

 (3 /i) nuclei which have apparently 12 chromosomes. They seldom 

 branch, (i) Digestion layer, which is bounded by an endodermis 

 provided with tannin and starch wherein is no infection. 



