SOIL FUNGI 275 



Primulaceae, Solanaceae (Nicotiana tobaccum, Solarium tuberosum, 

 Solarium nigrum), Scrophulariaceae, Compositae, Orchidaceae, etc. 

 The roots of various legumes are extensively invaded by a characteristic 

 fungus belonging to the mycorrhiza type. 149 The fungus is found in 

 the primary cortex and forms a coarse, nonseptate mycelium in the 

 roots and sends out haustoria into the deeper cells, often filling more 

 than half of the lumen of the cell. The fungus is well distributed in 

 the soil, and can infect most legumes (except Lupinus perennis and 

 two other plants) and various nonleguminous plants (Zea mays, Allium 

 cepa, Ipomoea purpurea, Verbascum thapsus, etc.). 



According to Melin, the fungus infection of the roots leads to their 

 shortening and development into mycorrhiza. The short roots are 

 branched in a characteristic manner, usually forklike. Mycorrhiza 

 formation takes place best in humus soils. 



Organisms responsible for mycorrhiza formation. Various species of 

 fungi have been reported to be able to live symbiotically with higher 

 plants. In the case of endotrophic mycorrhiza, mostly higher fungi 

 have been found. In many cases various Phycomycetes, including the 

 Mucorales, have been reported. In a few cases actinomyces and a 

 species of Penicillium were believed to be involved 150 although this 

 has not been established experimentally. According to Hagem, cer- 

 tain Mucorales, especially Zygorhynchus molleri, Mucor ramannianus, 

 certain species of Absidia (^4.. orchidis) and a green Penicillium may form 

 mycorrhiza with forest trees. Moller 151 also suggested the possibility 

 of formation of mycorrhiza by Zygorhynchus, an organism found to 

 form an abundant growth in sandy soils, especially in certain pine 

 barrens of New Jersey so as to practically hold the sand together in one 

 mass. MacDougal 152 believed that fungi belonging to Oomycetes, 

 Gasteromycetes, Hymenomycetes, and Pyrenomycetes can form mycor- 

 rhiza, but no experimental evidence was supplied. One must dis- 

 criminate carefully between attributions based merely on isolations of 

 species of fungi from mycorrhiza plants and those in which the mycor- 

 rhiza has been produced again experimentally by pure cultures of the 

 organisms. Positive proof of identity can only be supplied by inocu- 



149 Jones, F. R. A mycorrhizal fungus in the roots of legumes and some other 

 plants. Jour. Agr. Res., 29: 459-470. 1924. 



160 Peklo, 1913 (p. 270). 



151 Moller, A. Untersuchungen iiber ein und zweijahrige Kiefern im mark- 

 ischen Sandboden. Ztschr. Forst. u. Jagdwesen. 1903, H. 5-6. 



162 MacDougal, D. T. Symbiotic saprophytism. Ann. Bot., 13: 1-48. 1899. 



