Kelley — 50 — Mycotrophy 



in tracheids of the stele although they do not assume typical mycor- 

 rhizal form in these cells. Whether or not all this mycelium belongs 

 to the same fungus cannot be stated positively. Most of the mycelium 

 appears to be intracellular and typically endotrophic but there is some 

 evidence that it may be intercellular as well. A considerable number 

 of host cells contain a very dense aggregation of mycelium, while in 

 many of the host cells infected in this way the mycelium tends to 

 assume a nearly spherical form until finally the hyphae lose their 

 identity as individual strands and in some cells the entire mycelial 

 body appears as a nearly uniform amber-coloured sphere. This action 

 may have resulted from a plasmolysis of the entire contents of the 

 host-cell, or there is a possibility that phagocytosis has occurred. In 

 a few of the cortical cells there may be noted a number of larger 

 bodies varying from 15 to 33 /x in diameter, which are considered 

 tentatively as vesicles. 



Mycorrhiza of Fossil Lycopod: — One of the best known in- 

 stances of fossil mycorrhizae was described by Weiss (1904). A 

 mycorrhiza or perhaps a mycorrhizome was found in the Lower Coal 

 Measures, the root not being associated with the plant which bore it ; 

 but the plant was possibly Lycopodiaceous and was referred to the 

 form genus Rhisonium of Corda. Hyphae were found in root-hair 

 and in epidermis but for the most part in the inner cortex, where 

 hyphal swellings were found. The vesicles are usually empty but 

 sometimes contain homogenous contents. "The obvious resemblance 

 between these clumps in the fossil plant and those of recent mycor- 

 rhiza, together with the close agreement in the structure and behaviour 

 of the Fungus in the outer layers of the cortex with those of the 

 Fungus in recent mycorrhiza will, I think, be regarded as sufficient 

 evidence for the conclusion that we are dealing in the case of this 

 fossil plant with a mycorrhiza or a mycorrhizome. The Fungus differs 

 materially in its manifestations from other cases of endotrophic 

 mycorrhiza so far observed in fossil plants and in no case suggests 

 that it was living either saprophytically or parasitically upon the host 

 plant. The excellent preservation of both the Fungus and the host 

 plant and the specialization of the cortex into two layers comparable 

 with the Tilzwirtzellen' and 'Verdauungszellen' of recent mycorrhiza 

 would suggest that, as in the case of the latter, the host plant is deriv- 

 ing some benefit from presence of the Fungus." 



Mycorrhizae in a Seed Fern: — For the Pteridosperms or 

 Seed Ferns there is one record of possible mycorrhiza by Ellis 

 (1917). According to Ellis, in the fossilized vegetable remains of 



