The Algae 235 



cells. In the lowest algac the cells are quite independent of 

 one another, and in most of them dependence among the 

 cells of the plant body is very slight. That is, in most forms, 

 organs corresponding to the roots, stems, leaves, conducting 

 systems, and reproductive parts of higher plants are not 

 found, and all the cells in the plant body are much ahkc. 

 Under these conditions each cell must carry on for itself the 

 processes of absorption, photosynthesis, digestion, assimi- 

 lation, and respiration. So, when we speak of the alga3 as 

 simple plants, we mean only that they are simple in structure ; 

 in their physiological processes they may be very complex. 

 They all contain chlorophyll and are therefore capable of 

 manufacturing food. Some of them, however, grow better 

 in water that contains organic matter, and these forms doubt- 

 less get a part of their food directly from the organic sub- 

 stances in solution in the water. A good type with which to 

 begin a study of algae is Protococcus, a very common and ex- 

 tremely simple form. 



Protococcus. On the partly shaded, moist sides of trees, 

 rocks, buildings, and fences everywhere, there occur patches 

 that look as if they had been stained green. If a little of 

 this stain is scraped off and examined under a microscope, it 

 is seen to be made up of little rounded green cells. Each cell 

 has a cell wall, cytoplasm, and nucleus. In the cytoplasm is 

 a large green plastid which almost fills the cell. 



When the cells are examined, certain of them will be found 

 to be elongated ; some of these may be dividing into two. 

 Sometimes there are two or more cells still clinging together, 

 showing clearly that they have just been formed by division. 

 These groups separate readily when the cover glass is tapped, 

 and each single cell may go on living quite independently of 



