282 PRINCIPLES OF SOIL MICROBIOLOGY 



3. The fungi may take an active part in the decomposition of the 

 organic matter in the soil, thus making the nitrogen available for the 

 growth of higher plants, first suggested by Frank and later by Shanz 

 and Piemeisel, 180 who made a detailed study of the phenomenon of 

 fungus fairy rings. This is borne out particularly by the fact that 

 mycorrhiza are abundant in soils rich in organic matter; many of the 

 fungi, as the Basidiomycetes, found to be the causative agents of the 

 true mycorrhiza are capable of decomposing difficultly soluble organic 

 substances, such as woody tissues. They need not necessarily absorb 

 the organic matter but merely decompose it, liberating the minerals 

 and nitrogen, which are absorbed by the plant. According to Melin, 

 the role of mycorrhiza in the nutrition of trees and other plants growing 

 in peat (raw-humus), and similar soils, consists in obtaining the nutrients 

 from the soil organic matter and supplying it to the plants. In soils 

 with active nitrification, mycorrhiza formation is not essential for the 

 forest trees. Czapek was also of the opinion that the fungus obtains, 

 at least partly, its nutrients from the soil and not from the plant. 

 Burgeff found that plants infected with fungi were favorably influenced 

 in their ability to assimilate carbohydrates from the soil, when the 

 atmosphere was free from C0 2 . It thus became the general opinion 

 of the investigators 181 that the fungus provides the plant with nitrogen. 

 The fungus obtains its nitrogen from the soil organic matter, or it 

 synthesizes its proteins from the inorganic salts of the soil. The plant 

 is known to digest the fungus, just as in the case of insectivorous plants. 

 This intracellular digestion, which is conspicuous in the case of many 

 plants, may be merely a measure of resistance on the part of the vascular 

 plants, but since the products of digestion disappear, it may be assumed 

 that the plants absorb them (Nos. 118, 119, PL XV). 



4. A certain amount of evidence has been submitted to indicate that 

 the fungus may sometimes be injurious to the host plant. Gallaud 

 considered the fungus to lead an independent existence in the root 

 tissues, deriving all its food from the host plant and being an "internal 

 saprophyte." Bernard actually considered the fungus to be a parasite 

 which is subsequently checked in its development by the action of the 

 root cells; this confers a certain immunity upon the infected plant, the 

 process being one of phagocytosis. According to Detemer, the root 



180 Shanz, H. L., and Piemeisel, H. L. Fungus fairy rings in Eastern Colorado 

 and their effect on vegetation. Jour. Agr. Res., 11: 191-246. 1917. 



i8i Weyland, H. Zur Ernahrungsphysiologie mykotropher Pflanzen. Jahrb. 

 Wiss. Bot., 51: 1-80. 1912. 



