b-" 



THE FUNGI 243 



for an hour to a temperature of 149°-160° Fahrenheit 

 (65°-71° C). The spores resist a much greater heat. 



Light is unfavorable to the growth of bacteria in gen- 

 eral, and this is one important reason why living rooms 

 should be open to the sunshine. 



Dryness will not immediately kill bacteria, but it stops 

 their growth, and it is for this reason that evaporated fruits 

 and vegetables keep without decaying. In the case of 

 salted meats and fish, either smoked or not, the dryness 

 and the presence of ,-.',.,, 



much salt prevent decay. ,<.'->5'!:''---'y'.;>'vr,l'. 



Smoking adds some ere- <;'"''-'>,''~V-!;Tv.{'',i\V,;>''^~I: 



osote which is an addi- ^ 

 tional safeguard. Most 

 bacteria cannot grow in '-^.'^^'f•^V;/A'^;V?^'-t;^;"^"•;^l.^ 



the presence of much ~^;J;^}s^;^y\i'l^/^'>!-^' 



sugar or of vinegar, and "''■'>;"'?','•':;'',•','■'"'" 



this accounts for the ' 



1 • Vi- J! • u Fig. 170. Effect of Variations in Tern- 



keeping qualities of rich ^^^^^^^^ „^ ^^^^^^^ ^^^^^^_ 



preserves and iellies as . , ,. ^ • . -^ 



'^ •> u, a single bacterium; 6, its progeny in 



well as of pickles. twenty-four hours at 50° Fahrenheit; 



312. Reproduction.— ^' ^l^ f^^^l ''' t^^-^ty-fo^^ i^°"i-^ ^t 



'^ 70° Fahrenheit. 



Bacteria under ordinary 



circumstances reproduce by the division of the cells, each 

 parent cell forming two new ones. From this fact they 

 are often called fission fungi, . Fission goes on much faster 

 at rather high temperatures (Fig. 170). Resting spores 

 are formed by many species. The process of spore forma- 

 tion consists of the interior portion of the protoplasm 

 collecting into a minute ellipsoidal or globular mass which 

 becomes surrounded by a thick membrane. The spores 

 can survive high temperatures and extreme dryness, so 



