236 TEXTBOOK OF PLANT PHYSIOLOGY 



Besides organic nutrients, saprophytic microorganisms likewise 

 require mineral substances. To obtain a good development of 

 bacteria or molds it is necessary to supply approximately the same 

 mixture of anions and cations, as is commonly provided for higher 

 green plants. Particularly necessary are K, Mg, P, S, and Fe, 

 and often (especially for bacteria) Na and CI. The only excep- 

 tion is Ca, which is neccessary for the nutrition of green plants, but 

 is superfluous for fungi. The necessity of mineral salts for micro- 

 organisms was first shown by Pasteur (1860). Through the careful 

 and painstaking work of one of his students, Raulin, the mineral 

 nutrient requirements of the fungus, Aspergillus niger, was studied 

 in detail, and the classic composition of the solution necessary for 

 the optimum development of this fungus was given. It is as 

 follows: 70 g. cane sugar; 4 g. tartaric acid (to give an acid reac- 

 tion); 4g. NH4NO3; 0.6 g., NH 4 H 2 P0 4 ; 0.4 g., MgS0 4 ; 0.6 g., 

 H2CO3; 0.25 g. (NH 4 ) 2 S0 4 ; 0.07 g., FeS0 4 ; 0.07 g., ZnS0 4 , and 

 1500 cc. of water. Since then, it has been possible to simplify con- 

 siderably this solution. Zinc is not among the elements absolutely 

 necessary, but in its presence development proceeds more rapidly 

 and a higher total yield is obtained, but the development of fruiting 

 bodies is somewhat delayed. Raulin's solution shows clearly that 

 molds can develop very well on inorganic compounds of nitrogen, 

 which serve for the synthesis of its organic compounds. This capa- 

 city, which is also peculiar to yeasts, was made use of in Germany 

 during the World War, when a decided shortage of protein sub- 

 stances for the diet of the people was felt. Great quantities of yeast, 

 the cells of which are very rich in proteins, were cultivated on sugar 

 solutions with the addition of ammonia or urine, then washed and 

 dried, and mixed with flour. Bread baked from such flour had a 

 higher protein content and a high nutritive value. 



74. Nutrition of Parasites. Insectivorous Plants. — As has 

 been noted, there are almost no true saprophytes among the higher 

 plants; but among them are found a number of parasitic and semi- 

 parasitic forms, as, for instance, dodder (Cuscuta), broom rape 

 (Orobanche), mistletoe (Viscum, Phoradendron) , and others, which, 

 although they retain the basic characteristics of an autotrophic 

 plant, particularly the chlorophyll-bearing apparatus, nevertheless 

 secure a part of their food requirements from other organisms. 



In the figwort family (Scrophidariaceae) , especially the genera 

 Melampyrum, Alectorolophus, Euphrasia, Pedicularis, and others, 



