TYPES OF CRYPTOGAMS; THALLOPHYTES 213 
shown in Fig. 150, 2. They are also formed by the contents 
of spore-cases sub-dividing into many spores (Fig. 171, D). 
Spores are sometimes produced by the division of a mass 
of protoplasm into a small definite number of segments, 
often four. Spores which have the power of moving 
(swimining) freely are known as zodspores (Fig. 153, B). 
Fic. 150. Bacteria stained to show Cilia 
A, Bacillus subtilis; B, Bacillus typhi (the bacillus of typhoid fever) ; 
C, Bacillus tetani (the bacillus which causes lockjaw); D, Spirillum 
undula; E, Bacillus tetani forming spores. (All five are magnitied 
1000 diameters.) 
Sexually produced spores are formed in many ways. 
One of the simplest modes is that shown in Fig. 152, 
resulting in zygospores. Another method is illustrated in 
Fig. 156.1 
THE STUDY OF BACTERIA 
256. Occurrence. — * Bacteria may oecur anywhere but not every- 
where.’ In water, air, soil, and almost any organic substance. living 
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. 
267. 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. 
1 See Vines’s Students’ Text-Book of Botany, pp. 68-71. 
