382 MICROORGANISMS 



because some of these organisms are able to nourish themselves 

 on many materials which are not food for man. Plant organ- 

 isms which are thus able to nourish themselves on the non- 

 living bodies or products of animals and plants are known as 

 SAPROPHYTES. We have no special name for animals which 

 feed on like materials. 



I. SAPROPHYTES PLANTS WHICH LIVE UPON DEAD 

 ORGANIC MATTER 



434. Plant Relationships. It is a fact known to botanists 

 that the different kinds of plants which we see on the earth 

 today are actually related to one another much as the dif- 

 ferent individuals of a human family are related. That is, 

 the different kinds of plants which we see today and which 

 we commonly call SPECIES have all descended from a common 

 ancestry and therefore actually have " blood relationship, " 

 as we say. In the long ages which have passed since life be- 

 gan on the earth, plants have tended to vary in every possible 

 .direction and there have come to be many thousands of differ- 

 ent kinds, or species, of plants. Some of these species resemble 

 one another closely and are, therefore, closely related, while 

 others differ widely in their makeup. For convenience in the 

 study of plants, botanists have attempted to classify them 

 according to their actual relationships into groups of different 

 sizes. Thus, species that are closely related are put together 

 into groups called GENERA; the genera are combined into 

 FAMILIES, and the families are combined into larger groups. 

 The plants with which we shall be concerned in the present 

 chapter may, for our purposes, be grouped into three of these 

 larger groups. These groups are BACTERIA, YEASTS, and MOLDS. 



435. Classification of Plants. In classifying plants into 

 these larger groups, botanists rely mainly on the characters 

 which they show in connection with the process of reproduction. 

 Thus, the bacteria reproduce only by CELL DIVISION. Each 

 bacterium consists of only a single cell and reproduction is 

 accomplished by the single cell's dividing equally into two. 



