PART VI. REPRODUCTION AND CLASSIFICATION 



CHAPTER XX 



REPRODUCTION IN PLANTS AND ANIMALS 



Problems: What are some methods of asexual reproduction in 

 plants and animals f 



How is sexual reproduction in plants brought about? 

 What is the result of reproduction in flowering plants f 

 What are the methods of reproduction in simple animals ? 

 What is a metamorphosis and of what value is it f 

 What is the method of development in birds and mammals f 



Labokatory Suggestions 



Demonstration. Cell division. 



Demonstration. Grafting, layering, slipping in plants. The structure of 

 bulbs, corms, tubers, rootstocks, etc. P^egeneration in animal forms, if possible. 

 Class Exercise. Conjugation in spirogyra. 

 Demonstration. Growth of pollen tubes in sugar solutions. 

 Demonstration. Development of a simple animal. 

 Class Exercise. A study of the metamorphosis of insects. 

 Class Exercise. A study of the metamorphosis of a frog. 

 Demonstration or Home Project. Development of a chick. 



The Simplest Reproduction. — The simplest plants and animals, 

 composed of single cells, grow. But since they take in food and 

 oxygen and give off body wastes through their cell membranes and 

 walls, the size of the cell body is limited. This is because though 

 the volume grows in proportion to the cube of its diameter, the 

 surface grows according to the square of its diameter. Two 

 bricks cemented together have less surface 

 than two separate bricks. Therefore in order 

 to live the cell must get more surface. It 

 does this by cell division. 



Pleurococcus, a little green plant often found on tree trunks, 

 moist rocks, etc., is good to illustrate cell division in a simple 



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