298 MYCORRHIZAE AND MYCOTROPHY 



man (1942) indispensable in providing a knowledge of the present 

 status of studies on mycorrhizae. 



Occurrence of mycorrhizae. Formerly it was generally be- 

 lieved that relatively few species of plants possess mycorrhizae. 

 Alycorrhizal species were then regarded as objects of scientific 

 interest or even of curiosity. It is becoming more and more ap- 

 parent from cumulative records, however, that they involve a 

 wide variety of plants and that they occur widely throughout the 

 world. Mycorrhizae occur on trees, shrubs, and herbs on essen- 

 tially all kinds of soils ranging from the Arctic regions to the 

 tropics. In 1934 Asai [Burges (1936)] examined members of 134 

 families of plants in Japan and found mycorrhizae associated with 

 82% of them. McDougall and Glasgow (1929) found mycor- 

 rhizae in 28 species of composites. Samuel [Burges (1936)] re- 

 corded the occurrence of mycorrhizae in Australia on Euphor- 

 biaceae, Geraniaceae, Graminiaceae, Leguminosae, Liliaceae, 

 Mvrtaceae, Plantaginaceae, Ranunculaceae, Rosaceae, and Vio- 

 laceae. They have also been noted on members of the Burma- 

 niaceae, Cunoniaceae, Ericaceae, Epicridaceae, Lauraceae, Or- 

 chidaceae, Pyrolaceae, Rutaceae, and Sapindaceae [Burges 

 (1936)]. Nearly all species of coniferous and hardwood trees 

 examined have proved to be mycotrophic. Moreover, an ever- 

 increasing number of crop plants are being found to possess 

 mycorrhizae. 



The mycorrhizal habit is not restricted to the seed plants. 

 Fungal threads were noticed in the thalli of the liverwort, Preissia, 

 nearly 100 years ago. Since then, principally from the observa- 

 tions of Nemec in 1899, Galenkin in 1902, and Cavers in 1903 

 [Ravner (1927)], intracellular hyphae are of rather common oc- 

 currence within the rhizoids and ventral parts of the thalli in both 

 Jungermanniaceae and Marchantiaceae. Convincing proof of the 

 functional nature of this association, however, is lacking. Several 

 investigators have attempted to isolate each constituent in pure 

 culture in order to learn of the possible interdependence among 

 them. Such experiments have been uniformly unsuccessful, be- 

 cause it has been impossible to isolate the fungus on artificial 

 media. In consequence the opinion has been expressed that in the 

 Hepaticae mycorrhizae may be lacking and the associated fungi 

 mav indeed be highly specialized parasites. 



