GENERAL PRINCIPLES 11 



Organisms are divided into many groups, such as kingdoms 

 (e.g. plant and animal), subkingdoms, branches, classes, orders, 

 genera, and species. A species is "the smallest group of plants or 

 animals having certain characters in common that make them 

 different from all other plants or animals" (G. W. Hunter). 

 Species are grouped together into larger subdivisions called genera 

 (singular " genus"), etc. The scientific name of an organism gen- 

 erally consists of two words — the first signifying the genus and 

 the second the species, as, for instance, " Archeopteryx macroura," 

 which literally means " primitive winged creature with a long tail," 

 and is the name of the earth's first known Bird. 



I. Cryptogams 



1. Algae (e.g. Sea-weeds and Diatoms). 

 Plants. — f 1. Thallophytes \ 2. Fungi (e.g. Mushrooms). 



2. Bryophytes (e.g. Mosses), 

 f 1. Lycopods (e.g. Club-mosses). 



3. Pteridophytes ( 2. Equisetae (e.g. Horse-tails). 

 { 3. Filices (e.g. Ferns). 



(Cycadofilices, e.g. Seed-ferns), 

 f 1. Cycads. 



f 1. Gymnosperms ^ 2. Cordaites. 



II. Phanerogams f Conifers (e.g. Pines, Spruces, etc.). 



i 1. Monocotyledons (e.g. Grasses, Lil- 



[ 2. Angiosperms < ies, etc.). 



[ 2. Dicotyledons (e.g. Oaks, Roses, etc.). 



I. The Cryptogams comprise all of the flowerless and seedless 

 plants, the reproductive organs being single cells called spores. 



1. Thallophytes show "no definite axis of upward growth, and 

 no distinction of root, stem, and leaf. They all consist entirely 

 of cellular tissue, being entirely destitute of wood" (J. D. Dana). 

 In general there are two groups of Thallophytes — Algae and 

 Fungi — the former containing chlorophyl and able to live upon 

 inorganic substances, while the latter are without chlorophyl and 

 live upon organic matter. 



2. Bryophytes are like Thallophytes in being woodless, but they 

 develop a sort of axis of upward growth and possess leafy stems. 



3. Pteridophytes (Fig. 101) comprise the highest types of 

 non-flowering plants, and these have a clear distinction of root, 

 leaf, and stem, the stem possessing woody fibres. These plants 

 have been much more favorable for fossilization than most of the 

 foregoing, and they assume considerable importance in the fossil 



