386 The Ohio Naturalist [Vol. VI, No. 1, 



THE CLASSIFICATION OF PLANTS, II. 



JOHX H. SCHAFFNER. 



The three series of plants (Thallophyta, Archegoniata, and 

 Spermatophyta) fall into smaller groups which also represent a 

 succession of higher and higher stages of progressive develop- 

 ment. If the theory of evolution as accepted at present is sub- 

 stantially correct, it becomes evident that some forms of plant 

 life remained in the lowest condition from the beginning while 

 others advanced to higher and more complex stages. Why did 

 large numbers of species develop and continue until the present 

 time without advancing to any appreciable extent from the 

 starting point? The question can be answered by assuming 

 that groups of organisms varied and were specialized in a direc- 

 tion which interfered with further progress upward but not with 

 further variation along subordinate lines. Other groups varied 

 in a direction which led to higher possibilities without imposing 

 a barrier while still others passed back from a higher to a lower 

 condition. 



Based on the conception of vertical or progressive evolution, 

 the development of the plant kingdom may be arranged some- 

 what as follows: 



1. Genesis of living organisms. 



2. Primordial organisms or Archeophyta, supposed to have 

 been naked, amoebid cells of the simplest structure. 



o. Transition to encysted and wall cells of the types found 

 in the lowest plants of the present time. 



4. Nonsexual plants consisting of simple cells, masses, or 

 filaments. 



."). Development of sexuality or of conjugating organisms. 



(). The lower types of sexual plants. 



7. Gradual development of the higher and more complex 

 types, manv with a simple alternation of generations. 



8. The'hig:her Thallophytes. 



9. Transition to typical land plants and adaption to aerial 

 conditions. 



10. The lowest plants with a typical antithetic alternation 

 of generations and with a simple parasitic sporophyte. 



11. Gradual development of a more complex sporophyte. 



12. The higher plants with a well developed dependent 

 sporophyte. 



13. Transition to plants with an independent mature 

 sporophyte. 



14. Plants with homosporous sporophytcs with true roots, 

 leaves, and tibro-vascular tissue. 



15. Development of heterospory. 



