AQUATIC PLANTS USEFUL TO THE MICROSCOPIST. 59 



are shown in Fig. 14. The stem is brittle, and frag- 

 ments easily take root, so that the plant spreads rapidly. 

 Having been accidentally introduced into 

 England, it is said to have grown so fast 

 that it has choked up some of the shallow- 

 er streams and to have become a nuisance. 

 It is abundant in this its native country, 

 but it never acts so badly here. The whole chads cana- 

 plant is semitransparent, with leaves about 

 half an inch long springing directly from the stem, and 

 tapering to the point. These leaves, under the micro- 

 scope, exhibit a remarkable phenomenon. 



All plants are formed of cells, or cavities of various 

 sizes and shapes, surrounded on all sides by a delicate 

 membrane called the cell wall. The cells are seldom 

 empty. Their contents are chiefly the soft, colorless, 

 jelly-like substance called vegetable protoplasm, and the 

 small green grains (the chlorophyl) which give the 

 green color to the plant. In Andcharis the walls of 

 the leaf -cells are transparent, so that the microscope 

 shows a part of what is taking place within the cell ; and 

 it is a wonderful sight, for the protoplasm is slowly 

 moving around the walls, carrying the chlorophyl 

 grains with it. Up one side of that microscopic cell 

 travels the strange procession ; across, down, and up, 

 slowly and steadily the stream and the grains move 

 round and round. Sometimes a little thread of colorless 

 protoplasm leaves the main current and starts across by 

 a shorter road, and sometimes the current pauses, stops, 



