TYPES OF CRYPTOGAMS; THALLOPHYTES 



237 



of a central column. Have any of the branches free tips ? With a 

 power of 250 or more examine the spores. A much higher power 

 may be used to advantage. Describe the surface of the spore. 



THE STUDY OF BACTERIA 



263. Occurrence. " Bacteria may occur anywhere but not every- 

 where." In water, air, soil, and almost any organic substance, living 



FIG. 173. Spore-Cases of Slime Moulds. 



A, a group of spore-cases of Arcyria; , a spore-case of TricMa, bursting open 

 and exposing its spores to the wind, x 20 ; C, threads of the same, with spores 

 between them, x 250. 



or dead, some species of plant belonging to the group Bacteria may 

 occur. A small bunch of hay placed in a tumbler of water will, at a 

 suitable temperature, yield an abundant crop in a few days or hours. 

 Raw peas or beans soaked for a week or two in water in a warm 

 place will afford a plentiful supply. 



264. Cultures. Pure cultures of bacteria are commonly made in 

 some preparation of gelatine in sterilized test-tubes. Boiled potatoes 

 serve a good purpose for simple (but usually not pure) cultures. 



Select a few small roundish potatoes with skins entire and boil 

 in water for a sufficient time to cook them through. Cut them in 

 halves with a knife well scalded or sterilized, i.e., freed from all living 



