II. 



PROTOCOCCUS (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, 

 Protococcus is a spheroidal body -g-J-g- to 1-^-$ f an mcn * n 

 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 

 sometimes 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 \>y fission become 

 separate, 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. 



