RUBIDIUM SALTS. 33 



BEHAVIOR OF FUNGI TOWARD RUBIDIUM SALTS. 



It has long- been observed that mold fungi thrive in the presence of 

 even very small quantities of potassium salts, traces of which are 

 sometimes contained as impurities in certain organic compounds. 

 These traces have to be considered in preparing culture solutions for 

 special purposes. Yeast requires a larger amount of potassium, espe- 

 cially in the form of the primary and secondary phosphate, than do 

 mold fungi. Certain kinds of microbes, such as Anthrax bacilli, do not 

 develop well when the amount of potassium salts is very small. Sodium 

 salts can not replace potassium salts even for these simple organisms, 

 but rubidium salts can do so in certain cases, as in Bacillus coli, less 

 successfully in B.pyocy >aneus, a and still less in ( ladothrix. b The writer 

 has also established the fact that a mold fungus {Penicillium) and }^east 

 can utilize rubidium and caesium salts when the composition of the 

 nourishing solution is otherwise very favorable and contains sugar and 

 peptone. Giinther's observation that the behavior of different mold 

 fungi to rubidium salts varies is interesting, these salts being utilized 

 by Botrytis cinerea, butnot by Rhizopus nigricans. The less favorable 

 the organic nutrient is, however, the more will potassium show its 

 superiority over rubidium. The cultures of ( 'ladothrix and of Pen icil- 

 lium form floating masses in the solution containing potassium salts,'' 

 while they gradually sink to the bottom in those containing rubidium 

 salts. Further, spore formation is almost entirely prevented in 

 Penicillium when rubidium is offered in place of potassium. Only 

 after an increase of the magnesium sulphate a scanty formation of 

 spores was noticed. 



The secondary and primary phosphates are the most favorable forms 

 in which to oiler potassium salts to fungi. In case phosphoric acid is 

 applied as an ammonium salt, potassium may be added as lactate or 

 tartrate or as other assimilable organic salts. 



Finally, it may be mentioned that of all the alkali salts potassium 

 salts exert the most powerful positive chemotaxis upon bacteria, and 

 that next to them come rubidium salts (Pfefler). 



" Bot. Centralbl., 1898, No. 26. 



b Winogradzki has shown that Mycoderma vini al.su can utilize rubidium salts to 

 advantage, but not caesium salts. 



c Dissertation, Erlangen, 1897. 



''The writer prepared the culture solutions with the purest materials, consisting 

 in this case of — 



Per ecu I. 



Sodium acetate 0. 5 



Glucose 1.0 



Di-ammonium phosphate 1 



Magnesium sulphate 02 



Potassium tartrate 10 



26982— No. 45—08 3 



