I.] MICROSCOPIC PLANTS. j i 



examined were invariably charged with diatomaceous 

 remains, constituting a bank which stretches 200 

 miles north from the base of the Victoria Barrier, 

 while the average depth of water above it is 300 

 fathoms, or 1800 feet. Vast quantities, again, occur 

 in beds under the guise of a white powder, which is 

 called mountain meal, and is actually mixed with 

 flour in some parts of Sweden, though it is perfectly 

 inert, and can serve merely to increase the bulk of 

 the food." 



Mr. W. H. Shrubsole, F.G.S., has recently discovered 

 the presence of these ubiquitous organisms in the 

 London Clay formation. About 

 twenty species have already been 

 identified, but there are also a 

 number of species new to micro- FlG< I4 ' 



scopists. Mr. Shrubsole reports that he has traced 

 the diatomaceous zone for several miles, and is still 

 pursuing the inquiry. 



Some of the water-snails and other molluscs sub- 

 sist largely upon these Diatoms, and many rare 

 species have been obtained from the stomachs of 

 fish. They can endure the greatest degree of cold 

 without injury to their vital powers, and some have 

 been found in hot springs. 



All these plants we have mentioned belong to the 

 group of Algce ; they all possess chlorophyll^ and are 

 able to live upon the most simple chemical com- 

 pounds. We have next to glance at a group of 

 plants which never possess this chlorophyll, and can 

 only live on organised matter. To commence with, 

 we could not have a better subject than the Yeast- 



