342 Proceedings of the Royal Society of Edinburgh. [Sess. 
EXPLANATION OF PLATES. 
Plate I. Spirosoma ferrugineum, showing the beginnings of conidia-formation. 
Plate II. Nodofolium ferrugineum , with thick deposit of iron peroxide on 
surface, 
Plate III. Leptothrix Meyeri. The individuals are seen to be covered with a 
thick mass of iron peroxide. In this particular case the deposit has lost its- 
transparency. 
(Issued separately June 13, 1908.) 
