42 CELL GROUPINGS 



other than to neighboring cells, as a close inspection of Fig. 

 47 will show. 



If division occurs in two planes only, there may result the 

 above groupings and several others in addition. The four 

 cocci which result from a single division may remain 

 together, giving the tetracoccus or tetrad grouping. Very 

 rarely all the cocci divide evenly and the result is a regular 

 rectangular flat mass of cells, the total number of which is a 

 multiple of four. The term merismopedia (from a genus 

 of algae which grows the same way) is applied to such a 

 grouping. If the cells within a group after a few divisions 

 do not reproduce so rapidly (lack of food), as usually happens, 

 the number of cells becomes uneven or at least not neces- 



FiG. 47. — Long streptococcus Fig. 48. — Short streptococcus 



grouping. grouping. 



sarily a multiple of four and the resultant flat mass has an 

 irregular, uneven outline. This grouping is termed staphylo- 

 coccus {c!T(j.(r:uloz, staphylos = bunch of grapes) (Fig. 49). 

 It is the most common grouping among the cocci. 



When division occurs in all three planes, there is in addi- 

 tion to all the groupings possible to one- and two-plane divi- 

 sion a third grouping in which the cells are in solid packets, 

 multiples of eight. The name sarcina is applied to this 

 growth form (Fig. 50). The individual cells in a sarcina 

 packet never show the typical coccus form so long as they 

 remain together, but are alw^ays flattened on two or more 

 sides. 



The above descriptions indicate how the method of divi- 



