22 



BOTANY. 



ORDER I. Protococcacece. 



The members of this order are minute unicellular plants, 

 growing either in water or on the damp surfaces of stones, tree 

 trunks, etc. The plants sometimes grow isolated, but usually 

 the cells are united more or less regularly into colonies. 



A common representative of the order is the common green 

 slime, Protococcus (Fig. 11, A, C), which forms a dark green 

 slimy coating over stones, tree trunks, flower pots, etc. Owing 

 to their minute size the structure can only be made out with 

 the microscope. 

 A 



FIG. \\.-ProtococcacesB. A, C, Protococcus. A, single cells. B, cells divid- 

 ing by fission. C, successive steps in the process of internal cell division. s In 

 C iv, the young cells have mostly become free. D, a full-grown colony of 

 Pediastrum. E, a young colony still surrounded by the membrane of the 

 mother cell. F, Scenedesmus. All, x 300. G, small portion of a young 

 colony of the water net (Hydrodictyori) , x 150. 



Scraping off a little of the material mentioned into a drop of water upon 

 a slide, and carefully separating it with needles, a cover glass may be 

 placed over the preparation, and it is ready for examination. When 

 magnified, the green film is found to be composed of minute globular cells 

 of varying size, which may in places be found to be united into groups. 

 With a higher power, each cell (Fig. 11, A) is seen to have a distinct cell 

 wall, within which is colorless protoplasm. Careful examination shows 

 that the chlorophyll is confined to several roundish bodies that are not 

 usually in immediate contact with the wall of the cell. These green 

 masses are called chlorophyll bodies (chloroplasts). Toward the centre 



