CHAPTER XXIX 



REPRODUCTION IN PLANTS AND ANIMALS 



296. The meaning of reproduction. Thus far our discussions 

 of plants and animals have dealt with problems in nutrition. 

 In many ways those problems are of the greatest importance. 

 No matter how well nourished a plant or animal may be, its 

 kind will cease to exist on the earth unless there are means 

 by which new and younger individuals can be produced. The 

 process by which younger individuals are produced is known 



as reproduction (which means 

 " producing again "). 



In the bodies of plants 

 and animals the cells divide, 

 each cell forming two new 

 cells from one old one. This 

 is reproduction of cells. In 

 most plants and animals in- 

 crease in number of cells 

 and the enlargement that re- 

 sults is called growth, and 



not reproduction. Cell division results in reproduction in 

 the case of one-celled animals and plants, as in the bacteria. 



297. Reproduction of the yeast plant. The yeast plant con- 

 sists of a single spherical or oblong cell (fig. 125). It has a 

 simple wall within which are the living substances that con- 

 stitute the protoplasm. Yeasts get their food material from 

 the solutions in which sugar is dissolved, and in doing so 

 partially decompose the sugar; this partial decomposition 

 results in the production of alcohol. But when nutrition is 

 abundant the yeast plants enlarge and soon begin the 



270 



FIG. 125. Yeast plants 



a, a plant from which a bud has begun to 



grow; b and c, plants, each of which has 



two buds. Greatly enlarged 



