Lecture II — 31 — Occurrence of Mycorrhizae 



(1933). It is curious that trees so abundant as the hickories and so 

 comparatively important should have escaped attention. Likewise the 

 Betulas, for birches flourish in countries where mycorrhizal workers 

 live ; yet there is not much to report on them. The two more recent 

 studies, of Laitikari (1934) and of Bjorkman (1941) are con- 

 cerned with the root system in general and with the concomitant fungi. 



But with alder the case is different, for alder has "root excres- 

 censes" that attract curiosity; and two European species attracted 

 much attention in earlier days, Klecka (1935), Plotho (1941) 

 and Cernik (1937) being their modern students. Harshberger 

 was the only student of American alder while brief citations have 

 come for Japanese species. Plotho (1941) tried the synthesis of 

 alder nodules, which appears to be the only experimentation of the 

 sort on record. Two species of Carpinus are reported mycorrhizal, 

 the American species of Ostrya, and three species of Corylus. Com- 

 ing, then, to the Fagaceae we meet with beech which, for some rea- 

 son, has ever been popular at least in Europe, the latest study being 

 by Harley (1939). It was on beech that Meyen (1829) observed 

 his "pseudomorphose" of the roots which may have been an unwitting 

 discovery of mycorrhizae. Of chestnut, mycorrhizae were described 

 on the European species by earlier students who thought to find in 

 them a cause of disease of that economic tree. Chestnut provided 

 Kelley (1940) with his material for discovering the essential simi- 

 larity between blight and mycorrhizal infection. But the Californian 

 Castanopsis and Lithocarpus, with many species in Asia, are yet 

 untouched. The oaks {Qiiercus) include "more than 200 species" 

 of which 23 have been noted as mycorrhizal, one species only 

 (,Q. robur) having received some careful attention. Since oaks are 

 preeminently American they offer a splendid opportunity for study 

 of a vital function in important timber trees, especially open to those 

 who say they have the interest of forests at heart, — a field of re- 

 search that is virtually untouched. 



Elm (Ulmus) was noted by one of our earliest students, 

 Duhamel (1758), and since his time 5 species have been listed but 

 no detailed study of any member of this genus exists. A couple of 

 reports of "fungus-free" may be covered by Stahl's statement: 

 "Wenn auch feineren Ulmenwurzeln des Oefteren sich pilzfrei 

 erweisen, so trifft man doch hie und da innere Verpilzung." 

 McDouGALL (1928) and Janse (1897b) say that Celtis is mycorrhi- 

 zal, and AsAi reports the same for Zelkova (Abelicea hirta) but 

 otherwise nothing more is known of the mycorrhizae of the Ulmaceae. 

 Similarly, 3 species of Morus are reputed mycorrhizal, being, like 

 Ulmus, endotrophic; but we are as innocent of exact knowledge of 



