DESMIDS, DIATOMS, AND FKESH-WATER ALG.E. 69 



that the circulation takes place. It is a steady, quite 

 rapid flow, several currents streaming lengthwise up and 

 down the cell, carrying the minute starch grains and 

 other enclosed particles in their course. It has been 

 said that these currents sometimes enter the vacuoles, 

 and that the latter obtain their supply of swarming 

 granules from the particles in the streams ; it has also 

 been stated that occasionally one or more of the swarm- 

 ing granules leaves the vacuole, enters the current, and 

 journeys round the cell. These statements are rather 

 doubtful. But with a high -power objective (the one- 

 fifth, for instance) it is not difficult to select a granule, 

 and follow it as the current carries it down one side to 

 the vacuole, where, according to the writer's observation, 

 it never enters, but passes into an ascending current, 

 and continues the round. The vacuoles themselves are 

 visible with a good low-power objective, but to see the 

 swarming granules and the general cyclosis a one-fourth 

 or one-fifth is needed. 



In addition to the desmids and diatoms, almost every 

 pond and stream contains other minute plants of interest 

 to the microscopist, called the fresh-water Algae, which 

 he probably already knows, if not by this name, at least 

 by their general appearance, for they form those green 

 masses floating like a scum on the surface, or soft green 

 clouds attached to sticks and stones and dead leaves. 

 The Algse often have a disgusting appearance as they 

 collect in thick and heavy patches, but under the micro- 

 scope they reveal beauty undreamed of. All those slimy, 



