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LIVES OF PLANTS AND ANIMALS 



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Lichen on a rock. 



i. >F. Brownell 



How do lichens differ from other 

 plants ? 



tion prevails in our own 

 large intestine, where 

 certain types of useful 

 bacteria live. They help 

 keep down the putrefy- 

 ing bacteria while receiv- 

 ing a home and food in 

 return. Other examples 

 are the bacteria which 

 live symbiotically in the 

 roots of certain plants; 

 and the sea anemones 

 which are carried around 

 on the backs of some 

 hermit crabs to places 

 where food is plentiful, and they aid the crab in protecting it from 

 its enemies. In a general way the food relations between green 

 plants and animals may be said to show a symbiotic relationship, 



because the plants 

 could not make food 

 without the wastes 

 from the animals, 

 and the animals 

 could not exist with- 

 out foods made by 

 green plants. 



Parasitism. Not 

 all life is give and 

 take. Some plants 

 and animals live at 

 the expense of others, 

 giving nothing and 

 taking all. Such 

 plants and animals 

 'right pierce are known as para- 



Mistletoe on the branches of a sycamore tree. Notice that sites. Examples are 

 the branches to the left bear no leaves. They have been . 



killed by the parasite. seen in the dodder 



