REPRODUCTION BY MEANS OF SPORES ^^\ 



bacteria and which has given rise to the name splitting-fungi, 

 consists of a simple division of each cell into two similar halves, 

 each of which afterwards grows to an adult state and then repeats 

 the process (Fig. 261). 



In the cylindrical and spiral forms division takes place 

 almost always in one direction only, namely, across the cell, that 

 is at right angles to its long axis (a). The new individuals 

 produced may separate from each other as soon as the division is 

 completed, or they may remain attached to each other in larger 

 or smaller numbers : in the latter case long threads are produced. 



In the round or coccus forms, division takes place in one, two, 

 or three directions (b and c), so that if the individual cells remain 

 united with each other after their formation, threads, plates or • 

 cubical masses are produced. Those coccus forms which 

 divide in one direction only and remain attached to each other 

 in longer or shorter chains {¥", Fig. 261), are usually included 

 in the genus Streptococcus, those occurring in cubical masses 

 (d", Fig. 261) constitute the genus Sarcina, while the genus 

 Micrococcus embraces the forms which divide in two directions 

 {d". Fig. 261). 



The rate at which vegetative reproduction proceeds naturally 

 depends upon the temperature, nutrition, and other conditions 

 to which the organism is subjected, but under the most favour- 

 able circumstances many bacteria divide once or twice in an 

 hour, so that a single specimen multiplying at the latter rate, 

 for even a day, would give rise to several millions of new indi- 

 viduals. Unchecked growth of this kind rarely goes on for any 

 great length of time, for species are often antagonistic to each 

 other, food runs short, or the products of their activity accumu- 

 late and prevent further development. 



3. Reproduction by means of Spores. — Besides the vegetative 

 method of multiplication described above, many species of 

 bacteria form spores within their cells which are capable of 

 germinating and producing new organisms. 



