REPRODUCTION OF BACTERIA BY FISSION 19 



successive generations are all parallel. In this case, if the cells remain 

 attached to each other, unbranched chains arise as in Streptococcus pyogenes 

 (Fig. 10, a), a pus bacterium, or as in. Leuconostoc mesenteroides (Fig. 7, d). 

 If fission takes place alternately in two directions at right angles to one 

 another, flat tabular groups of cocci are produced, frequently quadrangular, 

 with four, sixteen, sixty-four cells and so forth. The red sulphur-coccus 

 ^hiopedia and Micrococcus (Pediococcus) tetragenus (Fig. 10) are examples 

 of this mode of growth. Finally, the planes of division may be formed in 

 three different directions successively, at right angles to each other, giving 

 origin, when the cells remain adherent, to cubical packets. The genus 

 Sarcina (Fig. i°, c) offers a typical instance of these. It is, of course, 

 possible to determine the manner of fission among cocci only when the 

 cells remain adherent to each other, or where successive generations are 

 held together by gelatinous exudations. If the cells separate after fission 

 their grouping gives no indication of the manner of division. 



»» O OO 



o 

 a. i. 



Fig. 10. Modes of fission among the coccaceae. a } Streptococcus pyogenes, planes of fission always parallel, 

 resulting in chains ; 6, Pediococctts tetragenus (Micrococcus tetragenus), fission alternately at Tight angles in two 

 planes, resulting in plate-like growths ; c, Sarcina iutea, fission in three planes at right angles to each other, resulting 

 in cubes or bale-shaped growths. 



There remains yet a.nother mode of increase conceivable, in which the 

 planes of division arise without definite sequence or relation to previous planes. 

 This would result in all manner of irregular cell-groups, above all in rami- 

 fications in one or more planes ; but there are no observations that would 

 prove the existence of such, and we can only conclude that irregular fission 

 does not take place. It seems likely that even in the great host of micro- 

 cocci (e. g. the Staphylococci of the pathologists) the splitting up of the 

 cells follows a fixed rule, but that their prompt severance from one another 

 prevents the formation of large groups. As far as the Staphylococci are 

 concerned, division probably occurs in the three dimensions alternately, 

 but not in regular sequence, so that after a few fissions in one plane a new 

 direction is taken at right angles to it, to be changed again soon for a 

 third. In this way we should get short chains, quadrate groups, and minute 

 cubical clusters side by side, and this is what actually occurs (Fig. 28, a). 



Spores and Sporulation (12). 



The bacterial cell, although able for a short time to resist the injurious 

 effect of an unfavourable environment (drought, changes of temperature) or 

 an insufficient food supply, cannot defy such influences for an unlimited 



c a 



