ESSENTIAL NONMETALLIC ELEMENTS 



101 



Fungi which utiUze only organic nitrogen. Certain fungi are unable to 

 utilize nitrogen except in the form of amino acids, peptides, and mixtures 

 of these compounds such as peptone. The use of organic nitrogen does 

 not extend to all organic compounds which contain this element. Many 



A B C D 



Fig. 17. Growth of two fungi on four media differing in nitrogen source. .4, no 

 nitrogen added; B, potassium nitrate; C, ammonium tartrate; D, asparagine. Above, 

 Helminthosporium sativum; below, Ceratostomella fimbriata. 



of the early reports claiming utilization of organic nitrogen only by various 

 species have been found to be in error. 



All the early work where peptone was the nitrogen source used is to be 

 suspected because the need for growth factors was not recognized. The 

 use of other complex nitrogen sources such as proteins makes interpreta- 

 tion doubtful for the same reason. However, in the case of amino-acid- 

 deficient fungi a portion of the nitrogen source must be supplied in the 



