274 



STRUCTURAL BOTANY 



wards cultivated by its discoverer in solutions of grape- 

 sugar, to which a little extract of meat had been added. 

 The formation of endospores characterises one great 

 group of Bacteria, and distinguishes them from similar 

 unicellular organisms. 



Bacillus suUilis, like most other living things, requires 



plenty of atmospheric 

 oxygen in order to flour- 

 ish. Some of the other 

 Bacteria, however, have 

 the remarkable peculiar- 

 ity that they thrive best 

 in the absence of free 

 oxygen. This is the case, 

 for example, with Bacillus 

 butyricus, the organism to 

 which the formation of 

 butyric acid by the fer- 



Fm. 107. Bacillus megatherium, a, mentation of sugar is due. 

 chain of vegetative rods, each con- T^ 4-Vn'ci POQP HTP OYVO-PTI 

 rating of two or more cells, but ln tniS CaS6 tfte OX 7g ei] 



septa not shown. Magnified 250. necessary for respiration 

 ^th^c r :l^lS: * not absorbed in the 



b, vegetative rods ; c-f, successive free state, but obtained 



stages in formation of endospores ; p ,-t i -\ j 



r, four-celled rod with ripe spores ; i rom the breaking down 



ffi-9a and &i ^ 2 > spores swelling O f the organic substance in 



before germination ; the mother cell- , . , ,, . v 



walls disappear ; k-m, germination wnicn the organism lives, 

 of spores. All figures except a It may be mentioned 



magnified 600. (After De Bary.) . . * 



here that numerous ex- 

 periments have proved that light has a very unfavourable 

 effect on Bacteria, completely stopping their growth and 

 multiplication in many cases, and even, when intense 

 enough, killing the cells outright. It is the rays towards 

 the violet end of the spectrum which exercise the 



