X. 



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 Protococcus. 

 In its vegetative condition Protococcus is a spheroidal body 

 iry^o" t^ Woo *^^ ^^ mQ}c\. in 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 some 

 small starch-grains are sometimes to be found in it. Certain 

 definite portions of the protoplasm, termed chromatophores, 

 contain a red or green colouring matter. The latter is 

 called chlorophyll. These chromatophores occupy a large 

 part of the cavity of the cell, so that under a low power the 

 whole contents appear to be coloured. 



Individual Protococci may be either green or red ; or half 

 green and half red \ or the red and green colours may co- 

 exist in any other proportion. 



In the middle of the cell is a distinct futcleus, containing 

 a nucleolus. 



^ The names Haematococcus, and Chlamydococcus pluvialis have 

 also been applied to this form, but it must not be confused with the 

 more ahunda.nt P/eurococcus which everywhere forms a green powdery 

 layer on trees, palings, &c. 



