292 SEMI-CENTENNIAL OF TORREY BOTANICAL CLUB 
Here also we see that while addition of zinc is necessary to 
bring about increased growth in Pyrex flasks, this increase in 
growth occurs in the cultures in Jena glass to which no zinc has 
been intentionally added. 
A comparison of the values obtained in these experiments will 
show the agreement in the dry weights of individual duplicate 
cultures, and of the mean values (average of five duplicate cultures) 
obtained in the different experiments. On the average the devia- 
tion from the mean does not exceed 0.040-0.050 gram, in excep- 
tional instances deviations of as much as 0.10-0.15 gram being 
encountered. This means, therefore, a variation of about 5 per 
cent for the zinc cultures and of 15 per cent for the zinc-free cul- 
tures, since the mean weight of the former is about 0.95 grams, of 
the latter 0.30 grams. 
e are therefore justified in concluding that while the addition 
of zinc serves to bring about an increased formation of dry weight 
in Kavalier Bohemian and Pyrex flasks, such increased formation 
of dry weight takes place in Jena flasks to which no zinc is inten- 
tionally added. That the increased growth that occurs in the 
Jena flasks is due to the solution of small amounts of zinc from 
the flasks is also highly probable in view of the presence of zinc 
in this glass. 
LIST OF PAPERS REFERRED TO IN TEXT 
1. Benecke, W. Die Bedeutung des Kaliums und des Magnesiums 
für Entwickelung und Wachstum des Aspergillus niger v. Th. 
sowie einiger anderer Pilzformen. Bot. Zeit. 54: 97. 1890. 
2. Coupin, Н. Sur la nutrition du Sterigmatocystis nigra. Compt. 
Rend. 136: 392. 1903. 
3. Javillier, M. Une cause d'erreur dans l'étude de l'action biologique 
des éléments chimiques: la présence de traces de zinc dans le 
verre. Compt. Rend. 158: 140. 1914. 
4. Javillier, M. Utilité du zinc pour le développement de Г Aspergillus 
niger cultivé sur milieux profonds. Bull. Soc. Chim. 
I5-16: 568. 1914 
5. Lepierre, C. Inutilité du zinc pour la culture de Г Aspergillus 
niger. Compt. Rend. 157: 876. 1913. 
ierre, C. Zinc et Aspergillus. Les expériences de M. Coupin 
et de M. Javillier. Compt. Rend. 158: 66. 1914. 
