ON THE MYCORHIZAS OF FOREST TREES 
63 
Moller (14) was usually ectotrophic but occasionally endotrophic; but 
neither of these authors found both forms in the same rootlet, and they 
had noevidence that both forms were due to the same fungus. Mangin 
(13) states that during the ten years he has studied mycorhizas he has 
never seen an ectotrophic filament within a root cell, but such a con- 
dition is found in the heterotrophic form. This mycorhiza may very 
well be considered an intermediate form between the ectotrophic and 
endotrophic mycorhizas. 
2. Mycorhizal Fungi and their Relation to the Chance Formation of 
Mycorhizas 
Very few attempts have been made to identify the fungi which 
cause ectotrophic mycorhizas, although it would seem an important 
work. Elaphomyces was reported by Rees (20) as causing ectotrophic 
mycorhizas on Pinus. Noack (16), who did more than any one else 
in this field, reported two species of Geaster causing mycorhizas on 
species of Pinus, two species of Tricholoma on Pinus and Fagus, two 
species of Lactarius on Fagus and Quercus, and three species of Cor- 
tinarius on Pinus, Fagus, and Quercus. Kauffman (9) has shown that 
Cortinarius rubipes Kauff. causes ectotrophic mycorhizas on Quercus 
rubra L., Acer saccharum Marsh., and Celastrus scandens L. Finally 
Pennington (18) has reported Boletus speciosus Frost and Tricholoma 
transmutans Pk. as mycorhiza formers on Quercus. With one excep- 
tion, Elaphomyces, these mycorhizal fungi are all Basidiomycetes, 
and the four that I have added to the known list are also Basidiomy- 
cetes. On the other hand, among the identified endotrophic mycorhiza 
fungi there has been reported only one Basidiomycete, Armillaria 
mellea, reported by Kusano (10) as forming endotrophic mycorhizas 
with Gastrodia elata. It is quite probable, therefore, that many of the 
common mushrooms are capable of forming ectotrophic mycorhizas 
with tree roots, but that very few, if any, of them form endotrophic 
mycorhizas with forest trees. Moreover, all those reported are late 
summer and autumn mushrooms. No spring mushrooms are known 
to be mycorhiza formers. 
The particular species of fungi and higher plants which may form 
mycorhizas with each other are not as limited as one might expect. 
MacDougal (11) states that a higher plant may form mycorhizas 
with only one or two species of fungi, but his observations were 
scarcely extensive enough to grant a positive conclusion to that 
