72 PHYSIOLOGY OF THE FUNGI 



furnishes the metal. The culture A^essels should be of quartz for work of 

 the most exacting kind, although Pyrex or other suitable glassware may 

 be used. It is desirable in any event to use a few quartz culture vessels as 

 controls. In part, the long controversy over the effect of zinc on fungi 

 was due to the liberation of sufficient amounts of this element from certain 

 kinds of glassware used as culture vessels. Javillier (1914) showed that 

 the addition of zinc to cultures of A . niger has little effect when Jena glass 

 culture flasks were used. When quartz vessels were used, the crop 

 increased from 291 mg. in the control without added zinc to 1,624 mg. 

 when zinc was added. Steinberg (1919) found essentially the same 

 results except that zinc deficiency could be demonstrated for A. niger 

 when Pyrex vessels were used (Table 10) . 



Table 10. The Average Weight of Five Cultures of Aspergillus niger Culti- 

 vated ON the Same Basal Medium in Three Makes of Glassware 

 (Steinberg, Am. Jour. Botany 6, 1919.) 



Make of glassware 



Jena 



Kavalier Bohemian . 

 Pyrex 



Mg. mycelium 



Zinc, 10 mg. per liter 



987 

 943 

 957 



Purification of culture media. Progress in the study of essential micro 

 elements depends upon methods of removing them from media. As long 

 as these elements occur in the ingredients of the media, their need may be 

 unnoticed and unsuspected. In 1919 Steinberg devised a useful method 

 of reducing the concentration of heavy metals, especially iron and zinc, in 

 media. In essentials, this method consists in autoclaving the complete 

 medium with 15 g. per liter of calcium carbonate. The hot solution after 

 autoclaving is filtered through paper or a fritted-glass filter, or allowed to 

 cool and the supernatant liquid decanted off. The precipitate must be 

 removed; otherwise the essential elements will be released by the fungi. 

 Calcium oxide and magnesium carbonate may replace calcium carbonate 

 in some applications (Steinberg, 193oa) . The mode of purification appears 

 to be as follows: During autoclaving, heavy-metal carbonates or their 

 hydroxides are formed. The excess calcium carbonate serves to adsorb 

 these insoluble compounds The composition of a medium is somewhat 

 changed by this treatment, part of the phosphate being removed as cal- 

 cium phosphate. In practice this is compensated by using an excess of 

 phosphate. A medium which is treated by this process is essentially 

 neutral in reaction, which may lead to some changes in the sugar during 

 autoclaving. 



