218 



PHYSIOLOGY OF THE FUNGI 



with increasing concentrations of copper the spores were yellow, yellow- 

 brown, gray-brown, brown, and black. 



The color of the spores produced on copper-deficient media by different 

 isolates of A. niger varied. Excellent correlation between the copper 

 content of various soils as determined by this method and the incidence 

 of copper deficiency in grain was found. Some of Mulder's results are 

 presented in Table 36. 



Table 3G. The Correlation of Copper Deficiency in White Oats and the 

 Copper Content of the Soil as Determined by Aspergillus niger Method 

 All soil was from the same field. (Mulder, Antonie van Leeuwenhock 6, 1940.) 



Available Copper, 

 Condition of Oats Mg per G. of Soil 



Severely diseased . 25 



Less severely diseased 0.8 



Healthy (from a portion of the field not showing the disease) 1.7 



Healthy (copper sulfate added to the soil) 2.5 



Magnesium. Smit and Mulder (1942) postulated that a microbio- 

 logical method would show better correlation with magnesium deficiency 

 in green plants than chemical methods. This was confirmed for the 

 Netherlands soils investigated. Azotobacter chroococcum and Aspergillus 

 niger were used as test organisms. Preference w^as given to the fungus 

 inasmuch as only 4 to 5 days w-ere required for an assay. A simple 

 technique was used, and visual comparison w^as sufficiently accurate to 

 diagnose magnesium deficiency in soils. 



Potassium. Aspergillus niger was used by Niklas and Toursel (1940) 

 to determine available potassium and other elements in soils. These 

 authors weighed the mycelium produced. Rogosa (1944) has shown that 

 Lactobacillus casei may be used to determine small amounts of potassium. 



rABLE 37. The Effect of Molybdenum Content of a Glucose-Nitrate Medium 



UPON Yield of Mycelium and Sporulation of Aspergillus niger 



(Mulder, Plant and Soil 1, 1948.) 



Molybdenum. The amount of this element needed by fungi and green 

 plants is greater when nitrogen is supplied as nitrate than when ammo- 

 nium nitrogen is furnished. This fact introduces a complication into the 

 microbiological assaj^ of molybdenum in that the sample must be ashed 



