§ III.] Endosporous Bacteria. 19 



but is not completed. All cells which do not take part in 

 the normal formation of spores ultimately die and are de- 

 composed, if they are not transferred in good time to a fresh 

 substratum. 



In other Bacilli, as B. Amylobacter, the procedure is dif- 

 ferent. Here spore-formation begins in single cells and spreads 

 by degrees to more and more of them, while a number of other 

 cells continue to vegetate and divide. We cannot therefore 

 regard the unsuitableness of the substratum to the vegetative 

 process as the cause which generally determines the formation 

 of spores. 



By spores are usually meant such cells as are delimited 

 from a plant to develope again under favourable conditions 

 into a new vegetating plant. The commencement of this 

 latter process is termed germination. The bodies to which we 

 have here given the name of spores are so called because their 

 behaviour corresponds to that of germinating spores. As soon 

 as they are fully grown, that is, as soon as they are ripe, the 

 membrane of the mother-cell dissolves gradually or swells, and 

 the spores are thus set at liberty, retaining the characters 

 which have been already described; that is, they are round, 

 ovoid, or rod-shaped, according to the species, rarely of some 

 other shape, with a dark outline and usually colourless, but 

 with a peculiar bluish glistening appearance ; according to Cohn 

 the spore of Bacillus erythrosporus is tinged with red. Round 

 the dark outline may often be perceived a very pale and 

 evidently soft gelatinous envelope, which either covers the 

 spore uniformly all round, or is thicker at the two extremities 

 and drawn out into processes. 



Germination shows that the spore is a cell surrounded by a 

 thin but very firm membrane, defined by the dark outline inside 

 the gelatinous envelope. Germination begins when the ripe 

 spore is subjected to the conditions favourable to the vege- 

 tation of the species, supply of water, suitable nutriment, and 

 favourable temperature. As it begins the spore loses its high 



c 2 



