REPRODUCTION IN PLANTS AND ANIMALS 271 



production of new plants. First there may be noted a small, 

 bud-like outgrowth on one side of the parent plant. This bud 

 enlarges for a time and finally becomes separated. The sepa- 

 rated bud is a new yeast plant, and after a brief period of 

 growth it may repeat the budding process by which it came 

 into existence. Indeed, sometimes a large bud, even before 

 it becomes separated from the parent, begins to form a small 

 bud for the production of the third plant in the series. 



Budding represents one of the simplest kinds of reproduc- 

 tion. This is known as vegetative reproduction, because 

 reproduction is accomplished by means of the ordinary nutri- 

 tive, or growing, part of the plant. Many simple animals are 

 reproduced in a similar way. 



298. Reproduction of pond scum. Almost everyone has ob- 

 served the common green " pond scum " floating upon the sur- 

 face of water or submerged. Some of these are very beautiful 

 plants when seen under the microscope. They are silky threads 

 composed of large cells joined end to end. Sometimes a thread- 

 like plant may become broken into two or more pieces, when 

 each piece may continue to grow as a new individual. This 

 is vegetative reproduction. 



Sometimes two of the pond-scum plants -which are near one 

 another perform quite a different kind of reproduction (fig. 126). 

 From two cells, one in each plant, there grow two tubular out- 

 growths. These grow toward one another and unite their tips. 

 They unite in such a way as to form a continuous tubular 

 passage between the cells. When this has been done, all the 

 living substance or protoplasm from one cell passes through 

 the tube into the other cell. The two masses of protoplasm 

 unite, and the mass thus formed becomes very compact and a 

 heavy wall develops closely about it. The old cell walls decay, 

 and the new dense cell goes to the bottom and passes through 

 a resting period which may last through the winter season. 

 At some later time the resting cell grows again, producing a 

 new plant like those that formed it. 



