260 BIOLOGICAL ACTIVITIES OF MOLDS 



the carbon-nitrogen ratio becomes wide. Increase of light, moder- 

 ate nitrogen starvation, or strangulation causes an excess of carbo- 

 hydrate. The mycorrhiza seems to remove this excess and so bene- 

 fit the plant. It acts as a parasite but only as long as the carbo- 

 hydrate is in excess, thus actually benefiting the plant by removing 

 the excess, but never as a parasite by removing the carbohydrate 

 when it is not in excess. Bacteriologists will note the resemblance of 

 this concept to that of the relationship of the legume plant and the 

 legume bacteria as suggested by Giobel. 



In some famihes of plants, e.g., the Orchidaceae (orchids) and 

 Ericaceae (heath plants), the mycorrhizal relationship is obligatory 

 for the normal development of the plants. In a few cases it has been 

 necessary to bring the fungus to the seedling crop plant where the 

 fungus was not found naturally in the soil. In orchids it is known 

 that the mycorrhizal fungi are necessary for the development of the 

 seedling. Soil from the natural habitat contains the fungus, hence 

 some of this is used in the seed bed. Knudson has shown that orchid 

 seedlings may be grown in a nutrient solution containing glucose, 

 until they have sufficient chlorophyll to synthesize their own car- 

 bohydrate without mycorrhiza. With these plants it is obvious 

 that the mycorrhiza has supplied the seedling orchid with carbo- 

 hydrate from the organic matter of the soil, making it available to 

 the seedling plant. There are possibly other ways in which mycor- 

 rhiza benefits other plants. For instance there is some evidence that 

 in some cases it takes part in the transformation and transfer of 

 organic nitrogenous soil materials from the soil to the growing plant. 

 In addition to Bjorkman's thesis * the reader is referred to mono- 

 graphs by Melin ^^ and Rayner.^° 



LITERATURE 



1. Bernhaxjer, K., Zum Problem dcr Saurebildung durch Aspergillus niger 



(Vorlaufige Mitteilung), Biochem. Z., 153, 517 (1924). 



2. Bernhauer, K., and N. Bockl, Zum Chemismus der durch Aspergillus niger 



bewirkten Saurebildungsvorgange. VII, Biochem. Z., 253, 16 (1932). 



3. Bernhaxjer, K., and A. Iglauer, tjber die Saurebildung aus Zucker durch 



As-pergillus niger, Biochem. Z., 286, 45 (1936). 



4. Bjorkman, E., tJber die Bedeutungen der Mykorrhizaabildung bei Kiefer 



und Fichte, Symb. Bot. Upsal, 6, No. 2 (1942). 



5. BoswoRTH, A., Chemical studies of Camembert cheese, N. Y. Agr. Exp. Sta. 



(Geneva) Tech. Bull. 5, 1907. 



6. Brierley, W. B., See Russell ei al.^^ 



7. Cahn, F. J., Citric acid fermentation on solid materials, Ind. Eng. Chem., 



27, 201 (1935). 



8. Calmette, a., German patent 146, 411, Oct. 3, 1921. 



