280 



PRINCIPLES OF SOIL MICROBIOLOGY 



For the study of the role of fungi in the germination of seed, Knudson used a 

 different method: 1.5 per cent of agar was added to one of the following nutrient 

 solutions: 



Ca(N0 3 ) 2 



K 2 HPO« 



MgS(V7H 2 0... 



KN0 3 



KC1 



FeCl 3 



Fe 2 (P0 4 ) 2 



(NH 4 ) 2 S0 4 



Distilled water 



pfbffer's 

 solution 



1 . gram 

 0.25 gram 

 0.25 gram 

 0.25 gram 

 0.12 gram 

 0.01 gram 



1000 cc. 



SOLUTION B 



1 . gram 

 0.25 gram 

 0.25 gram 



0.05 gram 

 0.50 gram 

 1000 cc. 



The medium is placed in tubes, 180 mm. by 18 mm.; the tubes are plugged with 

 cotton, autoclaved and slanted; the cotton plug is covered with a cap to 

 prevent contamination. The seeds are sterilized in calcium hypochlorite solu- 

 tion (10 grams in 140 cc. distilled water, shaking well and filtering), by covering 

 them several times in a test tube with the clear solution, for about 15 minutes. 

 By means of a sterile platinum needle the seeds are transferred upon the surface 

 of the sterile agar slope. The cultures are kept in moist chambers in the green- 

 house shaded by cheesecloth from direct sunlight. 



Role of mycorrhiza in the nutrition of plants. Various theories have 

 been suggested by different investigators in an attempt to explain the 

 role of the fungi in the nutrition of plants forming mycorrhiza. 



1. Symbiotic action between the hyphae of the fungus and the root 

 cells of the higher plants. Frank's 170 theory was that in ectotrophic 

 mycorrhiza the mycelial mantle takes the place and functions of the root 

 hairs; the fungus absorbs the mineral salts and nitrogenous materials 

 from the soil organic matter, while the host plant supplies the fungus 

 with carbohydrates. At first, Frank claimed a similar role for the 

 endotrophic mycorrhiza, but since the endophyte has little connec- 

 tion with the exterior of the plant, the above theory was modified to 

 state that the plant procures the nitrogen by digesting the fungus. 

 Stahl 171 also suggested that there is a relation between the low trans- 

 piring powers of the plant and the presence of the mycorrhiza fungi 

 in the roots, the latter supplying the former with mineral salts obtained 



170 Frank, 1885 (p. 271). 



171 Stahl, 1900 (p. 273). 



