56 VEGETATIVE REPRODUCTION BY FISSION. 



short and joined broadside on, the attached sides measuring 2. i p 

 each, whereas the length of each is only 1.3 //,. This microbe, 

 therefore, exhibits both styles of fission. On the other hand, 

 longitudinal fission alone is manifested in a fission fungus dis- 

 covered by METSCHNIKOFF (I.), and named Pasteuria ramosa, 

 which grows in the ventral cavity of certain water-fleas (Daphnia 

 pulex and D. magna), where it produces 

 a fatal disease. In these microbes the new 

 septum is always longitudinal. 



In the separation process now under 

 consideration, wherein the division of the 

 mother-cell and the casting off of the 

 daughter-cell take place in one direction 

 only, the number of mother- and daughter- 

 cells is always equal ; the total number (e) 

 of cells obtained from the initial cell (a) at 

 the end of the n ih reproduction being : 



FIG. 12 Bacillus 



tumescens. 



a, and b, chains of short 

 members. (After A. 

 Koch.) Magn. noo. 



= 2 n a. 



A much greater rate of increase is 

 attained in a given time when the sub- 

 division is effected in several directions simultaneously. Examples 

 are known of both possible events, viz., separation in two, and 

 separation in three directions at right angles to one another. 



43. Division in Two Directions. 



In this case the cell contents subdivide into four parts by the 

 formation of two septa intersecting each other at right angles, and 

 each splitting into two lamellae, whereupon the mother-cell be- 

 comes four daughter-cells. The latter again undergo subdivision, 

 whereby 4 x 4 = 16 cells are formed. At the end of n sub- 

 divisions, the total number of cells from a individuals will be 



e = 4"a = 2 2 "a, 



In this case, where the separation goes on continuously in two 

 directions perpendicular to one another, and so always in the same 

 plane, there results provided the gradually extending cells retain 

 their connection a mosaic-like stratified plate which has been 

 named Merismopedium (divided plate). A coccus exhibiting this 

 method of reproduction is known as a pediococcus. To this group 

 belongs the lactic-acid-producing Pediococcus acidi lactici discovered 

 by Paul Lindner. 



