42 MINERAL NUTRIENT MATERIALS. 



rubidium salt from the accompanying potassium salts. This 

 difficulty is, moreover, accentviated by the comparatively ready 

 solubility (even at simple boiling temperature) of the glass of 

 the culture vessels, the consequence being that a little alkali 

 finds its way into the nutiient solution from the glass during 

 the sterilising process. In order to eliminate this soui'ce of 

 error several workers have already recommended the use of 

 metallic culture vessels for the purpose in question, but soon 

 had to abandon same on account of the toxic action and conse- 

 quent retardation of development produced on the sowing. This 

 was observed, in the case of silver, by Raulin (III.), whose similar 

 observation in the case of tin was confirmed by W. Benecke (III.). 

 This last-named worker also excluded aluminium from the list 

 of sviitable metals, for the reason that it sustained corx-osion and 

 therefore caused an alteration of the nutrient solution, although 

 Th. Bokorny (I.) employed it, apparently with good results, in 

 his experiments on the nutrition of aJgce. Finally platinum, 

 which, according to Bokorny, has a poisonous effect on the 

 green thallophytes in question, was found by Benecke to be 

 innocuous in the case of Aqjeryillus viijer ; it is, however, too 

 expensive to use for large series of experiments. The difficulties 

 encountered in purifying the nutrient salts, in order that the 

 experiments conducted therewith may be perfectly reliable, can 

 best be appreciated by the aid of the following data, for which 

 we are indebted to W. Benecke (II.) and E. Guenther (I.). 

 The figuies relate to the minimum quantity of KCl which will 

 enable the development of the sowing to proceed when added 

 to loo c.c. of a nutrient solution previously free from potash. 

 Aspergillus niger is sensitive to 0.02 mg., Rhizopns nigricans to 

 0.0 1 mg,, Mucor corymbifer to 0.02 mg., and Botrytis cinerea to 

 0.0 1 mg. of KCl. The essential requirements of the fungi in 

 respect of potash are therefore very moderate ; and, in fact, if 

 the necessary quantity be exceeded, to the extent of several 

 units per cent., the growth may be injured. The maximum 

 amount of potash salts which Rhizopus nigricans will stand, and 

 still continue not only to grow but also to fructify, has been 

 determined by E. Guentuer (I.) as follows: KCl, about 7.5 

 per cent. ; KNO3, a,bout 7 percent. ; whilst in the case of K.,SO^ 

 the organism will still bear up to 10 per cent, (concentrated solu- 

 tion) very well. 



In opposition to the concordant results obtained by earlier 

 workers, Carl Wehmer (IV.) assumed that sodium is able to 

 replace potassium as a nutrient material for fungi. This view 

 was, however, disproved by the experiments of W. Benecke 

 (III.) on Asjiergillus itiger, an undescribed species of PeniciUium, 

 Mucw stolonifer, Botrytis cinerea, and a pure-culture wine yeast 

 from Winningen ; these results being also strengthened by 

 E. Guenxher's (I.) culture experiments with Mucor corymbifer , 



