TYPES OF CRYPTOGAMS; THALLOPHYTES 237 
of a central column. MHave any of the branches free tips? Witha 
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.” Jn water, air, soil, and almost any organic substance, living 
FiGc. 173. — Spore-Cases of Slime Moulds. 
A, a group of spore-cases of Arcyria; B,aspore-case of Trichia, 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 teniperature, 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 
