THE CELL. 45 



Life History and Morphology. Protococcus vulgaris, Green Pro- 

 tococcus, is a spherical organism ranging in size from 1-10,000 to 

 1-350 of an inch in diameter. It consists of a cell-wall (cellulose), 

 protoplasm, nucleus, and nucleolus. Within the cell the protoplasm 

 is in green-colored masses containing chlorophyl. These are the 

 cliromato'phores, or ehloroplasts. Multiplication takes place by fis- 

 sion. The protoplasm divides first; then a partition is formed be- 

 tween the two portions, and the cells thus formed separate. 

 Often, however, before the new cells separate, one or both 

 may again divide, thus forming groups of three or four cells; these 

 also may be subject to fission, so that groups of six, eight, etc., may 

 occur, the number generally being some multiple of two. There are 

 two states of protococcus: The quiescent, just described; and the 

 motile form, which is ovoidal in shape and is provided with two 

 ftagella which, by their contraction, give to the cell a whirling mo- 

 tion. This state of protococcus is called a zoospore. In course of 

 time the zoospore loses its flagella and becomes a quiescent cell. 



Protococcus pluvialis is found in the gutters of houses, and dif- 

 fers from the foregoing in possessing a small amount of red pig- 

 ment. It, also, reproduces by endospores. The protoplasm of the 

 resting cell divides into four portions or into many portions, in the 

 former case producing megazoospores, and in the latter, microzo- 

 ospores. These are set free by the bursting of the wall of the parent 

 cell. 



Protococcus nivalis is the so-called red snow of Arctic regions. 



Habitat. Protococcus vulgaris is found on brick, rocks, fences, 

 houses, and the bark of trees. 



Laboratory exercise No. 7. Protococcus. From the north side of a 

 tree or fence obtain some bark or wood containing' a coating' of green 

 Protoccecus. Moisten and place under a bell jar or in a Petri dish for 

 twenty-four hours in a warm place. When the cells have begun to vege- 

 tate, apply the surface of a cover-glass. Some of the cells will adhere. 

 Add a small drop of water if necessary, and examine with H. P. Ob- 

 serve the shape, color, and size of the cells. Find a single cell; then 

 one with a partition showing normal fission. Find also a triplet and 

 groups of four, eight, etc. Search now for motile forms. These are the 

 zoospores. Irrigate your preparation with acetic acid, and discover, if 

 possible, a nucleus. Make drawings illustrating a single cell, doublets, 

 triplets, and groups of four or more; also zoospores. 



