APPENDIX A 



Grouping of Plants and Animals 



We separate all the forms of living things we know into "plants" and "animals" 

 without any effort. All except a very few of the plant species have chlorophyl, and 

 all but a few remain in a fixed place. All the others we call animals, although there 

 are many species of animals that do not roam about. Some natural objects, however, 

 are unmistakably "living" and yet are not so easily classed as plants or animals. We 

 have seen that a "virus" resembles a chemical compound rather than a complex 

 living structure (see page 444) ; and yet a virus increases in quantity at the expense 

 of suitable "food", just as growing protoplasm does. 



Other living forms that lie between plants and animals are the so-called "slime 

 molds", or Myxomycetes, which are sometimes classified as true fungi. In the active, 

 or vegetative, state the organism consists of a large mass of naked protoplasm con- 

 taining numerous nuclei. This mass moves about in an ameboid fashion, and is nega- 

 tively phototropic. When exposed to drying or to light, it develops rather complex 

 spore- bearing structures, resembling some of the molds. 



Pleuiocoocua 



>*r^Protopldst escaping 

 \ —^S^^ injm spore 



Flagellate stages 



Plasmodium 



Slemonitia 



Sporangium ^ Stauiastnim MiciasteriM 



• Xanthidium 



Euglena 



Euglena is an example of a group of one-celled chlorophyl-bearing organisms that 

 are sometimes classed with the green algae (see illustration, below). But these 

 species have distinct "animal" traits. In the whiplike flagellum, or swimming lash, 

 the organism resembles the flagellate protozoa. In its method of swallowing food, 

 it resembles the ameba. Yet it is useful and convenient to think of living species in 

 these two main divisions — plants and animals. 



Most of the names used in classifying plants and animals are Latin or Latin in 

 form. In these outlines all Latin names have been anglicized to facilitate their 

 pronunciation except where the Latin form is as easy or as familiar. 



The outlines are, of course, not complete. The subdivisions have been carried 

 only as far as students are likely to need them. Groups which are of little interest 

 to any except the professional taxonomist have been either treated by a special 

 note or omitted entirely. 



The successive subdivisions in the plant-and-animal classification scheme are 

 shown on pages 40 and 41; the "relatedness" of the various branches is shown in 

 the frontispiece. 



687 



