306 A TEXTBOOK OF GENERAL BOTANY 
the bacteria have nuclei seems to depend largely on the defi- 
nition of nucleus. If the term nucleus is confined to highly 
organized nuclei which divide mitotically, then the bacteria do 
not appear to have nuclei. If, on the other hand, granules which 
have staining properties resembling those of chromatin may be 
regarded as nuclei, some bacteria possess such structures. Cer- 
tainly the bacteria do not seem to possess anything that resem- 
bles a typical nucleus. 
Decay bacteria. The 
remains of plants and 
animals do not decay 
by themselves but are 
destroyed by the action 
of other organisms. We 
know that fruit and 
meat decay very rap- 
idly if no care is taken 
to prevent this process. 
_ That the decay is not 
due to anything inher- 
ent in the substances 
themselves is shown by 
the process of canning, 
as when we sterilize 
milk, meat, or fruit by heat and then seal them in cans. The 
reason why these substances do not decay under such conditions 
is that by heating we kill all the living organisms that would 
destroy them, while by sealing we prevent the access of other 
organisms. Decay may be due either to bacteria or to fungi, 
which are also plants without chlorophyll. ) 
In the growth of green plants and of animals large quan- 
tities of important chemical elements are stored up in organic 
compounds. When plants or animals die, the elements in these 
organic compounds are not immediately available to green plants 
but must first be reduced to simple inorganic compounds. In 
causing the decay of organic remains and thus returning the 

Fig. 309. Internal structure of bacteria 
Redrawn after Dobell 
