Kelley — 30 — Mycotrophy 



Mycorrhizae in Gnetaceae: — There are but two references to 

 the possible mycorrhizal condition of these plants : ( 1 ) Strasburger 

 said that root hairs are exceptional in Ephedra, while (2) Kirch ner 

 remarked that root fungus was not observed by von Tubeuf and that 

 root-hairs are not exceptional but found covering the roots for a dis- 

 tance of 2-3 mm. 



The Method of Opportunism: — To summarize what is known 

 of the mycorrhizae of Gymnosperms, therefore, one must say that 

 much is known of a few pines and spruce and larch but that there is 

 no general research upon the occurrence of mycorrhizae in the class as 

 a whole. The same method of opportunism rules with the Angio- 

 sperms : there have been few scientific approaches to the mycorrhizae 

 of higher plants through a systematic investigation of their occurrence. 

 A few papers such as those of Janse and of Schwarz point the way 

 to a more thoroughgoing study of the rooting structures of Angio- 

 sperms ; and meanwhile one pieces together the isolated papers to 

 form the following picture. 



Mycorrhizae in Apetalae: — First as to that collection chiefly of 

 trees which has been called the Apetalae one notes that many are re- 

 corded mycorrhizal ; indeed, the oaks and beeches are, with the pines, 

 much studied plants. Of the poplars and aspens, Popiilus, seven 

 species have been studied although not in much detail but their my- 

 corrhizal character is established: KleCka and Vukolov (1935) are 

 their only modern students. Sixteen species of Salix are given a 

 similar character by various reporters, Klecka and Asai being the 

 most recent. The Garryaceae are unreported, for Mexico and the 

 West Coast are almost untouched mycorrhizal fields. But the Myri- 

 caceae are much investigated because of their root-nodules which are 

 true consortia (or mycodomatia), being occupied by bacteria and 

 fungi simultaneously; and they are present in all members of the 

 genus that have been studied — which are five of the 35 listed for the 

 genus. Most of the work on Myrica has been done in Europe and 

 Asia, almost none in America ; but the American Comptonia is listed, 

 by Kellerman. Leitneria, monotypic genus of the Corkwood family 

 is unreported, and so, too, are the Asiatic Platycarya and Pterocarya; 

 but the walnuts (Juglans) are recorded mycorrhizal. It is to be 

 observed that Frank and Stahl both stated that /. regia is not 

 mycorrhizal, KleCka (1935) calls it ectotrophic, while the few 

 reports on the two American species term these latter endotrophic. 

 No detailed study of the walnuts is in print, nor of the hickories 

 (Carya) except for that of the pecan (C pecan) by Woodroof 



