SECT. I 



CRYPTOGAMS 



335 



from a single point either as a single flagellum (monotrichous) or 

 as a group (lophotrichous). A single, polar fiagellum occurs in 

 Vibrio cholerae (Fig. 242, a) ; a polar terminal tuft of flagella in Spiril- 

 lum undula (Fig. 242, b, d) ; a lateral tuft in the swarm-spores of 

 Cladothrix (Fig. 243). The ciliary tufts may become so closely inter- 

 twined as to present the appearance of a single thick flagellum. The 

 cilia are never drawn within the body of the cell, but undergo 

 dissolution before the formation of spores takes place, or under 

 unfavourable conditions (Fig. 242, e). 



Multiplication of the individual is accomplished vegetatively by 

 the active division or fission of the cells ; the preservation and dis- 



FiG. 242. — Types of arrangement of flagella. a, 

 Vibrio cholerae ; h, d, Spirillum undula ; d, 

 development of a new bunch of cilia in divi- 

 sion ; c, Bacillus typhi ; e, Bacillus subtilis. 

 (After A. Fischer, x 2250.) 



Fig. 243. — Cladothrix dichotoma Formation 

 of swarm cells from the cells of the fila- 

 ment. (After A. Fischer,- x 1000.) 



tribution of the species by the asexual formation of resting spores. 

 These arise as endospores (Figs. 244, e, 246, e, f) in the middle or 

 at one end of a cell by the inner portion of the protoplasm separat- 

 ing itself from the peripheral, and surrounding itself with a thick 

 membrane. The membrane of the mother cell becomes swollen and 

 disintegrated when the spore is ripe. Spores are not found in all 

 species. 



Bacillus suUilis, the Hay bacillus (Fig. 244), which ai)pears as a rule in the 

 decoction obtained by boiling hay in water, will afford an example of the life- 

 history of a Bacterium. The spores of this species, Avhich withstand the effect of 

 the boiling water, produce on germination rod-shaped swarming cells with cilia on 

 all sides ; these divide and may remain connected in short chains. At the surface 

 of the fluid these swarming cells change into non-motile cells without cilia, which 

 divide up, giving rise to long intertwined chains of cells. These are associated 

 together in the pellicle covering the surface (zoogloea stage). Spore formation 

 occurs when the nutritive substances in the fluid are exhausted. 



Although the cycle of forms passed through in the life-history of a Bacterium 

 is a very simple one, the individual species, which can often be barely dis- 

 tinguished by morphological characters, show great variety in their metabolic 

 processes and in their mode of life. The majority of Bacteria require oxygen for 



