II. 



PEOTOCOCCUS (Protococcus pluvialis). 



IF the mud which accumulates in roof-gutters, water- 

 butts, and shallow pools, be collected, it will be found to 

 contain, among many other organisms, specimens of Pro- 

 tococcus. In one of the two conditions in which it occurs, Pro- 



tococcus is a spheroidal body ^. to of an inch iD 



JLuuUO 



diameter, composed, like Torula, of a structureless tough 

 transparent wall, inclosing viscid and granular protoplasm. 

 The chief solid constituent of the cell-wall is cellulose. The 

 protoplasm contains a nitrogenous substance, doubtless of a 

 proteinaceous nature, though its exact composition has not 

 been determined, and indications of starchy matter are some- 

 times to be found in it. Either diffused through it, or collected 

 in granules, is a red or green colouring matter (Chlorophyll). 

 Individual Protococci may be either green or red; or half 

 green and half red; or the red and green colours may coexist 

 in any other proportion. 



In addition to the single cells, others are found divided by 

 partitions, continuous with the cellulose wall, into two or more 

 portions, and the cells thus produced "by fission become sepa- 

 rate, and grow to the size of that form from which they started. 

 In this manner Protococcus multiplies with very great rapidity. 

 Multiplication by gemmation in the mode observed in 

 Torula is said to occur, but is certainly of rare occurrence. 



