386 



General Botany 



serves more readily than canned fruits, and canned fruits more 

 readily than fruit juices to which no sugar has been added. The 



Fig. 243. The carbon cycle in nature. Bacteria and other saprophytes play 

 role opposite to that of the green plants. 



first has a high concentration of sugar, the last a low concentra- 

 tion. Bacteria develop very slowly in the first medium and very 

 rapidly in the last. In the laboratory, bacteria are cultivated 

 on gelatine or on agar (seaweed jelly) plates. Many bacteria 

 grow very slowly when the water content of the gelatine falls 

 below 50 per cent. If the medium on which they live dries out, 

 all the vegetative cells become inactive and death gradually 



