EVOLUTION OF PLANTS 389 



of embryos is known as the doctrine of recapitulation or the bio- 

 genetic law. It states that the organism, in the course of its 

 growth as an embryo, goes through stages similar to those through 

 which the whole race has developed. This theory was first ex- 

 pressed by Professor Haeckel, a German embryologist. Remember 

 three words ontogeny recapitulates phylogeny. Ontogeny is 

 the history of an individual ; recapitulates means repeats ; phy- 

 logeny, the history of the entire race or group. 



Evolution of plants. It is thought that plants, too, have gone 

 through an evolutionary series, but because they have little in the 

 way of skeletons to fossilize, less is known about their early his- 

 tory than about animals. Early vegetation consisted of luxurious 

 growths of mosses and ferns. One descendant of these primitive 

 fern groups is called the giant Equisetum or horsetail. It is com- 

 monly found growing along railroad embankments. This vegeta- 

 tion died, decayed, and collected to a depth many feet in thickness. 

 It became buried beneath newly deposited soil and was later 

 pressed and heated by volcanic action. Ancient forms of bog 

 mosses formed peat. Prehistoric ferns and allied plants formed the 

 basis of our present-day coal deposits. Some fossils of the forms 

 of vegetation then growing are preserved in the coal. The earlier 

 plant forms had certain primitive forms of fibrovascular bundles. 

 Many modern plants, though they have developed a more complex 

 form, grow the primitive form first. Later came the seed-bearing 

 plants. 



QUESTIONS AND SUGGESTIONS 



1. What is evolution ? 



2. What are some of the ideas on evolution held by ancient scien- 

 tists ? 



3. Discuss the use and disuse theory of the origin of species. 



4. Discuss the natural selection theory of the origin of species. 



5. Discuss the mutation theory of the origin of species. 



6. What practical difference does it make which theory of evolu- 

 tion proves to be true ? 



