ECTOTROPHIU MYCOItHIZA. 97 



After the mycorhiza have functioned as such for some thue, 

 the fungoid sheath, as well as the hyphae contained in the 

 cortex of the root outside the endodermis, are thrown off by 

 internal cork-formation. This is, however, not always the case, 

 for the fungus may penetrate further and develop injurious para- 

 sitic characteristics; this is so with Pohjsnccum} and Eldphomijcr^ir 



Endotrophic Mycorhiza. 



(1) On non-chlorophyllous plants living in humus. 



Certain Orchideae — N'rottin Nidus <ivis, Epipogon (Jindini, 

 Goodyent rcpcns, etc., as well as some Gentianeae,^ possess 

 roots developed as endotrophic mycorhiza. In Coralliorhiza the 

 fungus frequents the short coral-like rhizomes. The fungus in 

 these cases penetrates into the cells of the root-cortex, and 

 there forms a l)all or coil of hypliae ; it neither covers the 

 roots externally nor inhabits the epidermal cells, so that the 

 production of root-hairs goes on quite normally. From the 

 circumstance that the hyplial coils become emptied and only 

 the remains of walls are left in the still living root-cells, Frank 

 concludes that the fungus after being nourished for a time by 

 the root-cells is ultimately deprived of its contents by them. 

 On this account he calls these roots " fungus-traps," and the 

 plants possessing them " fungus-digesting plants." It must be 

 remarked, however, that the fungus grows onwards from older 

 parts of the roots to younger, so that here, as in many other 

 cases, the contents of the hyphae may pass from tlie older into 

 the younger hyphae. Frank himself suggests* the possibility 

 that the roots take up nutriment without aid from the enclosed 

 fungus, and also that the latter receives its food parasitically 

 from the former. What advantage the roots may receive from 

 reabsorption of food, which they have previously supplied to the 

 fungus, has not been closely investigated, nor has the question 

 whether the roots are in a prtsition to nourish the ])laiits equally 

 well without fungi. 



The root-fungi of Orchideae have long been known, and Pfetler-'* 



' Biuns, "Beitrag z. Kenntniss il. Gattung Polysaccum," Flora, 1S94. 

 - Reess, " Uiitersuch. iiber d. Hirschtrtiffel," Bibliofj. Botaii. 1887. 

 ^ Primj'iheim's Jahrbuch, xvi. ami xx. 

 * Frank, Lehrbitch d. Botaiiik p. 2(57. ■' Landirirth. Jahrhiich, 1877. 



