192 



Tetrasporineae 



incrustation in the temperate climates of the northern and southern hemi- 

 spheres, generally on the windward side of tree-trunks, palings, stones, walls, 

 etc. The cell-walls are strong and of some thickness, and the Alga is able 

 to withstand considerable desiccation. The products of cell-division do not 

 separate readily, so that compact groups of 2, 4, or 8 cells are frequent 

 (fig. 118-4). The cells contain a single much-lobed parietal chloroplast, which 

 appears sometimes as several parietal cushions and at other times is so 

 massive as to fill almost the whole cell. Normally the chloroplast is without 

 a pyrenoid, but a pyrenoid has often been described and figured as occurring 

 in certain of the cells (see fig. 118 A, py}, although it yet remains to be 

 decided how far these records are correct 1 . Under certain conditions, usually 



Fig. 118. A, Protococcus viridis Ag. ( = ' Pleurococcus vulgar is Menegh. 1 of most modern 

 authors). B, P. rufescens Kiitz. var. sanguineus (W. & G. S. West) . All x 520. 

 chl, chloroplast ; p, protoderma-state ; pa, palmella-state ; pg, red pigment (hoematochrome?) 

 dissolved in globule of oil ; py, pyrenoid. 



of excessive moisture, short filaments of cells are formed which exhibit a 

 simple type of branching. This form, which is almost entirely a culture- 

 state and was described by Snow ('99) as ' Pseudopleurococcus,' greatly 

 resembles the genus Protoderma and is known as the ' protoderma-state.' 

 A ' palmella-state ' may also be developed in cultures. Reproduction occurs 

 by the formation of one or many aplanospores. Zoogonidia and isogametes 



in future be used in the sense of Oltmanns ('04), West ('04), Chodat ('09) or Wille ('09). This 

 may seem undesirable, but the facts are so clear that the change must be made, and the sooner 

 the better. 



1 It is possible that some of these records really refer to the initial stages of species of 

 Prasiola, the cells of which are grouped in a manner very similar to their arrangement in the 

 small colonies of Protococcus viridix. Each cell has, however, an axile stellate chloroplast with 

 a central pyrenoid. 



