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Our Surroundings 



bacteria, called nitrogen-fixing bacteria, which grow on some 

 plants. These bacteria change the nitrogen into soluble nitrates, 



valuable plant food, which root 

 hairs, or tiny rootlets of the 

 plants, absorb. 



For centuries past, farmers 

 have noticed that crops raised 

 on soil which has borne clover 

 or other members of the legume, 

 or pod-bearing, family during 

 the preceding year are always 

 especially prolific. The reason 

 for this has now been learned. 

 Investigators discovered on the 

 roots of the plants of this fam- 

 ily slight enlargements called 

 tubercles, or nodules, which 

 contain vast numbers of nitro- 

 gen-fixing bacteria. These ni- 

 trogen-fixing bacteria are of in- 

 valuable service to farmers in 

 feeding plants on which they 

 live and in enriching the soil 

 for other crops. 



Other Forms of Bacteria. There are also forms of bacteria 

 that are useful to the dairyman, as they develop desirable flavors 

 in butter and cheese. These foods are said to ripen when they 

 have been subject to the action of such bacteria. 



Other bacteria are helpful in manufacturing processes. Cer- 

 tain varieties soften the useless woody parts of hemp and jute, 

 so that the fibers used in making rope are released. Others 

 release the flax fibers needed in the making of linen. Other bac- 

 teria eat out the harder parts of animal hides, so that they may 

 be made into soft and pliable leather. Still other bacteria im- 

 prove sponges by ridding them of a slimy waste. 



Yeast. Other forms of plant life, somewhat similar to bac- 

 teria, are the yeasts. They are useful in making bread. After 



ROOTS OF A POD-BEARING PLANT 

 SHOWING NODULES 



