182 



BOTANICAL GAZETTE 



[march 



In about 200 preliminary cultures it was found that the addition of 

 small quantities of acids such as HC1, HNO„ and H 2 S0 4 had a 

 stimulating effect on the growth of Penicillium. This is only an 

 instance of the general rule that poisonous substances act as stimu- 

 lants when given in sufficiently dilute concentration. These two 

 series were carried through with great care and uniformity, in order 

 to get, if possible, a more accurate quantitative statement of the facts 

 noted in the preliminary cultures. There is considerable individual 

 difference in the cultures, as is noted by reading the figures in each 

 column, the five cultures being duplicates of one another. Neverthe- 

 less, they are of the same general magnitude. The addition of min- 

 eral acids produces a decided stimulation of growth. The nitric acid 

 in each case gave a greater stimulation than the hydrochloric. The 

 sulfuric acid in one case {table II) gave a greater increase than hydro- 

 chloric, while in the other case (table III) its effect was about equal 

 to that of the HC1. These observations agree with those made on the 

 preliminary cultures. Many of the cultures seemed to show that 

 nitric and sulfuric acids produced greater stimulation than hydro- 

 chloric acid. It was thought possible that HC1 might begin to act 

 as a poison at the concentration used, but a series of cultures (table IV) 

 showed that the optimum for stimulation was much higher than 0.004W. 

 Therefore HC1 at that concentration cannot act as a poison, but is 

 actually a milder stimulant than HN0 3 , and perhaps also weaker than 

 H 2 S0 4 . In addition to the usual mineral nutrients, the cultures in 

 tables II, III, and IV were given o.25 gm KC1 per ioo cc of culture 

 fluid, to avoid the introduction of a new ion, CI, in the cultures to 

 which HC1 was added. None of the alcohol cultures produced spores. 



TABLE IV 

 Each flask received 0.69?™ alcohol = concentration 0.3 GM. per liter. 



