12 PLANT LIFE. 



a filament. As the cells are either spherical or rod-like, the 

 shape of the colony depends upon the shape of the compo- 

 nent cells and the way in which they divide (see ^f 24). 



17. Gelatin. — In the fission-fungi, as in the fission-algae, 

 considerable masses of gelatinous material are produced, in 

 which the cells may lie embedded. The films, sometimes 

 smooth, sometimes wrinkled, which appear on an infusion of 

 organic matter, are formed by the masses of bacteria which 

 become embedded in the gelatinous material produced by 

 the alteration of their cell-walls {b, fig. 16). 



18. Cilia. — Most species are furnished with locomotor 

 organs consisting of fine threads of cytoplasm protruded 

 through the wall, which, by their sudden contraction on one 

 side, lash about like whips, and propel the cell by jerky, 

 darting motions through the fluid in which it swims. These 

 lashes, called cilia, may be single at the ends of the cell 

 (C, fig. 17), or many at ends or sides (A, fig. 17), or the 







Fig. 17. — Bacteria stained to show cilia. A, cilia tufted at one end; B, cilia irregu- 

 larly distributed over body; C, cilium single at one or both ends. B, the bacillus 

 of typhoid fever; C, the bacillus of Asiatic cholera. Magnified 775 diam.— After 

 Migula. 



whole cell may be covered with them like hairs (B, fig. 17). 

 They may be withdrawn or drop off when the plant comes 

 to rest, as when they form the scums previously mentioned. 



These plants are most interesting on account of their 

 economic relation to health and disease, decay, fermentation, 

 etc., which cannot be discussed here.* 



* For further information on these plants, see Frankland : Our 

 Secret Friends and Foes ; Prudden : Story of the Bacteria, Dust and 



