CRYPTOGAMS 



309 



pigment, measure only - 0005 mm. in diameter, while the rod-shaped 

 cells of the Tubercle Fungus, Bacillus Tuberculosis, are only from O'OOIS 

 mm. to - 005 mm. long. 



The simplest form of Fission-Fungi are represented by minute 

 spherical cells, Cocoi. Forms consisting of short, rod-shaped cells are 

 designated Bacterium ; those of the same shape but longer are known 

 as Bacillus. Simple cell filaments are termed Leptothrix ; spiral, 

 closely-wound filaments are classified as Spirillum, when more loosely 

 wound as Vibrio, and longer spiral filaments as Spirochete. In the 

 highest stage of their development the Fission-Fungi consist of cell 

 filaments exhibiting false branching, as in certain of the Nostocaceae. 

 As in the Fission-Algae, but more frequently, the cell walls become 

 swollen and mucilaginous. In this condition of their development, 

 termed Zooglcea, the Cocci, Bacilli, etc., appear to be embedded in a 

 gelatinous mass, as in the Alga Nostoc. 



While most Bacteria have only one form throughout the whole 

 course of their growth, and are accordingly spoken of as species of the 

 genera Micrococcus, Bacterium, Bacillus, etc., there are, on the other hand, 

 so-called pleomorphic species which exhibit differences of form cor- 

 responding to different stages in their life-history. 



Multiplication of the individual is accomplished vegetatively by 

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

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

 Bacteria may be divided into the follow- 

 ing two groups, according to their mode 

 of spore-formation : — 



1. Arthrosporous Bacteria, in 

 which vegetative cells, just as in the case 

 of Nostoc (Fig. 227), simply become thick- 

 walled and converted into spores (cf. 

 Leuconostoc, Fig. 231, E). 



2. Endosporous Bacteria, in which 

 the spores are formed within the cells by 

 the contraction of the protoplasm and its 

 investment with a new cell wall {cf. 



Bacillus subtilis, Fig. 230, B). 



Many Bacteria are motile. Their in- 

 dependent movements are due to the 

 vibration and contraction of fine proto- 

 plasmic cilia. These flagella, according to 

 A. Fischer, are distributed over the whole 

 surface of the cells (e.g. Bacillus subtilis, 

 Fig. 228, and also the Typhus Bacillus), 

 or they are polar, and spring from a single 

 point. A single, polar flagellum occurs in Vibrio cholerae ; a polar 

 terminal tuft of flagella in Bacterium termo ; a lateral polar tuft 



Fig. 22S. — Bacillus subtilis. Swarming 

 rods with numerous fine flagella. 

 Spores cultivated in an infusion 

 of hay, A, after 7 \ hours ; B, after 

 8 J hours, with fully -developed 

 flagella. (After A. Fischer, x 

 1500.) 



