INTRODUCTION 33 
so useful in the preparation of culture-media for 
observing the growth of bacteria. The same species, 
together with another (Gracilaria confervoides, and 
probably also species of Huchewma) are used by the 
Chinese and Japanese for making jellies and sweet- 
meats, and for stiffening purposes, varnishes, Wc. 
The extensive deposits of fossil Diatoms which 
occur in several quarters of the world furnish in 
some cases valuable polishing powders, and are used, 
as in the case of the Hanoverian Kieselguhr deposit, 
for mixture with nitroglycerine to form dynamite. 
