THE FUNGI | 369 
return to the vegetative form and then are capable of multiplica- 
tion by fission in the ordinary way. 
Two kinds of spores occur amongst bacteria, arthrospores and 
endospores, Arthrospores represent entire bacterial — vegetative 
cells which lose some of their water and thicken their walls and 
thus become resting cells. Endospores or true spores of bacteria 
are formed within the cell. They have the power of resisting a 
greater heat than the arthrospores. 
Rapipity oF GRowTH AND MULTIPLIcATION.—The rapidity 
with which bacteria grow and multiply is dependent upon species 
and environment. The rapidity of the growth is surprising. 
Under favorable conditions they may elongate and divide every 
Fic. 273.—Spores and their location in bacterial cells. (Marshall after Frost and 
McCampbell.) : 
twenty or thirty minutes. If they should continue to reproduce 
at this rate for twenty-four hours, a single individual would have 
17 million descendants. If each of these should continue to grow 
at the same rate, each would have in twenty-four hours more, 
17 million offspring, and then the numbers would develop 
beyond conception. However, such multiplication is not 
possible under natural or even artificial conditions, both on 
account of lack of nutritive material and because of the inhibition 
of the growth of the bacteria by their own products. If they did 
multiply at this rate, in a few days there would be no room in the 
world but for bacteria. 
CHEMICAL CoMpPosITION OF BAcTERIA.—The quantitative 
chemical composition of bacteria is subject to wide variations, 
dependent upon the nutritive material furnished them. About 
eee: 
