108 BOTANY. 



naked masses of protoplasm again, thus completing the 

 round of life (Fig. 45). 



There are seven orders of Slime-moulds, which are distinguished 

 mainly by their structure in the spore-bearing stage. Many species 

 occur in all parts of tlie United States, and may be readily found on 

 decaying logs, stumps, etc., and on the bark-covered ground in tan- 

 yards. A fine large one — Fuligo varians — is especially common in 

 the last-named situation. 



Class II. Bactbkia {Schizomycetes). 



221. The plants of this class are minute cells, each con- 

 sisting of a mass of protoplasm surrounded by a thin wall. 

 The cells cohere but little, and in some cases not at all. 

 They contain no chlorophyll, and always live in solutions 

 of nourishing matter. The Bacteria include many genera 

 and species. The Yeast-plants, commonly associated with 

 them, are in fact reduced Sac-fungi (p. 1'76). 



222. Bacteria. — These are the smallest of living things. 

 Their minute cells in some cases measure no more than 

 .0005 mm. {-^^-^ inch) in diameter. They are in some 

 species rounded in shape, in others elongated like little 

 rods, or in others more or less curved (Fig. 46). They are 

 frequently provided with one or two cilia (i.e., whip-like 

 projections of protoplasm), by means of which they move 

 about with great activity. 



223. Bacteria are found in great numbers in the watery 

 parts of decaying organic matter, causing various kinds of 

 fermentation. They reproduce by fission with such aston- 

 ishing rapidity that in a short time they swarm in any ex- 

 posed substance which is capable of furnishing them with 

 food. Some of the species; live in the watery juices of 

 plants and animals, causing various diseases. 



234, Som^ bacteria can endure high temperatures, and 



