82 Lectures on Bacteria. [$ vm. 



observers, they share this part with other plants which are green 

 and are related to the Oscillatorieae and Ulothricheae (25, p. 769). 

 The forms which have now been described are the largest, 

 but by no means the only, representatives of the aquatic Bac- 

 terium-flora. 



The Spirilla which live in bog-water are remarkable forms, 

 and may be briefly illustrated here by two examples. Spirillum 

 Undula, Cohn (Fig. 8, A), forms small spirally-twisted rods of about 

 i p. in thickness. The width of the spiral in dead specimens is 

 about 3 ft, three times therefore the diameter of the cell, the height 



of a turn of the spiral 5-6 n 

 (4-5 ^ according to Cohn). 

 Each individual is usually 

 formed of from ii to 2 



turns only of the spiral ; 



p. 8 when it has reached this 



length it divides transverse- 

 ly in the middle into two. According to Cohn 3 turns of the 

 spiral are only rarely attained. The rod consists of segment- 

 cells, which, as far as can be determined, are immediately after 

 division about as long as a half turn ; they separate from one 

 another as soon as they are of this size (a\ or after longer 

 growth. 



Spirillum tenue, Cohn (Fig. 8, J5), is more slender and more 

 closely twisted than S. Undula, and has several connected turns 

 of the spiral, usually 3, 4, or 6. The length of each of the 

 segment-cells which compose the spiral is at the time of division, 

 as far as I was able to determine, about half a turn, the same 

 therefore as in S. Undula. 



No other phenomena of development than growth and division 

 of the rods have been perceived in these two species, even during 

 a cultivation of some months' duration; they both remain 



Fig. 8. A Spirillum Undula, Cohn ; at a separation into two segment- 

 cells. B Spirillum tenue, Cohn; three specimens of different lengths. 

 Magn. 600-700 times. 



