48 MINERAL NUTRIENT MATERIALS. 



oxidases, by reason of the convertibility of its protoxide, this 

 being readily oxidised to peroxide, which in turn as readily 

 parts with oxygen and is reduced to the protoxide. Consequently, 

 in Bertraxd's (VI.) opinion, the organic constituents of the 

 oxidases merely play the part of carriers of manganese. For 

 the purpose in view, this latter cannot be replaced by any allied 

 or other metal. 



According to the results obtained by Richards (I.) in cul- 

 ture experiments with Asjjenjillu.^ m'ger, aluminium is not only 

 non-essential as a foodstuff, but has no appreciable action as a 

 stimulant. 



§ 231.— Sulphur, Selenium, Silicon, Phosphorus, 



Arsenic. 



Strictly speaking, it has not yet been proved that sulphur is 

 essential to the growth of fungi ; that it is so having been con- 

 cluded from the (still disputed) assumption that this element 

 forms an important constituent of the albuminoids. The 

 attempts hitherto made to carry out perfectly convincing ex- 

 periments, in nutrient media, positively free from sulphur, 

 have proved futile. Thus, neither Adolf Mayer nor E. 

 GuENTUER (I.) succeeded in fully eliminating this element from 

 the saccharose vised in the preparation of nutrient solutions, 

 a few thousandths of a per cent, remaining in combination as 

 an ineradicable impurity. According to the investigations of 

 Nsegeli, sulphates as well as sulphites and hyposulphites may 

 serve as a source of sulphur ; but ammonium thiocyanate and 

 sulphurea are unsuitable. A careful confirmation of this report 

 is the more desirable because Adolf Mayer, in his cultures of 

 beer yeast, found sulphates unsuitable for this purpose. 



Selenium appears to be incapable of replacing its near ally, 

 sulphur, as a nutrient material for fungi. At any rate, the 

 experiments of E. Guenthek (I.) with Rhizopus nigricans have 

 shown that an addition of even 0.0005 P®^' cent, of sodium 

 selenate will suffice to prevent the germination of spores of 

 this fungus in a nutrient solution of glycerin and mineral 

 salts. 



Silicon also, according to J. Raulix (III.), must be included 

 in the list of foodstuffs essential to fungi, though no support to 

 this view is afforded by the later cultivation expei-iments con- 

 ducted on this point by H. M. Richards (I.). Nevertheless — 

 in view of the observation (unfoi'tunately not followed up) of 

 E. Wixtersteix (I.) that the ash of his so-called fungocellulose 

 (§ 225) consisted almost exclusively of silica — it may be regarded 

 as not impossible that silica (as is undoubtedly the case in the 

 higher plants), while not e^senfial to the structure of fungi is 

 very useful for strengthening their membranes. The present 



