761 
être suffisant a la formation des conidies.’’ On the contrary the 
greater the proportion of the quantity of mould material with respect 
to the manganese present, the smaller the production of spores. 
This explanation is not, however, in accordance with my obser- 
vations as the produced quantity of mould was only very little 
increased by the addition of zinc. 
But like BerrranD [ have observed that by adding manganese, in 
spite of the presence of zine, the production of spores is furthered. 
Notwithstanding Brertranp’s excellent investigation only few of the 
factors are known which determine the formation of spores. 
It is proved, however, that in the hitherto treated cases siackening 
of the spore formation is combined with a great plastic aeguivalent 
of the carbon. 
6. Substitution of rubidium to potassium. 
In 1879 Náeert') made some experiments with rubidium and 
caesium *) on the metabolism of Aspergillus niger from which he con- 
cluded that these elements could replace potassium. 
BENECKE *’, who studied this question more in detail, proved that 
by replacing potassium by rubidium the production of mycelium was 
normal, but that sporeformation was inhibited. 
He found that the dry weights of the rubidium moulds at the 
lower Rb.concentrations were somewhat higher, in other cases again 
lower than those obtained ina medium containing potassium. In stronger 
concentrations rubidium retarded the growth and only insignificant 
coats of mould appeared which did produce spores, which fact BENECKE 
could not account for. Probably the presence of potassium, if large 
quantities of rubidium salt are used, then becomes of importance in 
relation to the small weight of mycelium. 
The results obtained by NdAcri1 and Bryecke are here chiefly 
confirmed as appears from wkat follows. 
If instead of potassiumchloride rubidiumchlorid is used the formation 
of mycelium remains the same. The “rubidium moulds’, however, 
are distinguished from those cultivated with potassium by their being 
1) G. v. Näaerem, Sitzungsberichte d. math. phys. Classe d. k. b. Akad. d. Wiss. 
zu München vom 5 Juli 1879, 
2) I have proved that caesium cannot replace potassium. 
3) W. Benecke, Ein Beitrag zur mineralischen Nahrung der Pflanzen, Ber. d. 
deutschen botan. Gesellschaft 1894 S. 105. 
Die zur Ernährung der Schimmelpilze notwendigen Metalle, Jahrbticher fiir wis- 
senschaftliche Botanik Bd. 28 (1895) S. 487. 
