300 The Ohio Naturalist. [Vol. V, No. 5, 



dryland plants the water taken from the soil into the bodv of the 

 plant is sufficient for carrying on all the essential processes of life. 



From certain morphological characteristics the three great 

 groups or series have been called Thallopiiyta, Archegoniata, 

 and Spermatophyta, or in English, Thallophytes, Archegoniates, 

 and Spermatophytes or Seed Plants. It must not be supposed, 

 however, that all plants live in the habitat to which thev seem to 

 have been adapted originally. The great inajorit}' of Thallo- 

 phytes now live in the air, many Archegoniates are found in verv 

 dry places, while great numbers of Seed Plants have returned to 

 the water. 



The general progress of the history of the earth's surface has 

 been from an aqueous condition to a dry land condition. Plants 

 originated in the water and since islands and continents arose 

 from the primordial ocean they have been stranded on the shores 

 and crowded from water to aerial conditions bv the clrving of 

 swamps and seas. When drier conditions began to prevail on 

 the enlarging islands and continents, the lack of free water was 

 met by the development of seeds. The progressive advance- 

 ment of the general mass of the plant kingdom has plainlv been 

 along the lines of the earth's physiographic history. It must not 

 be concluded however, that the evolution of plants was entirely 

 or even to a considerable extent due to environment but only 

 that the evolutionary process has kept pace with physiographic 

 changes on the earth. The evolutionary processes are primarilv 

 the result of protoplasmic properties and functions. Organisms 

 in the past were as well adapted to live in their environment as 

 organisms are at present ; and from a geological point of view it 

 becomes evident that evolution has been making its wav through 

 the conditions of environment from the beginning. Generalized 

 or archaic types are usually as rare in fossil groups as among liv- 

 ing forms. As for example in various groups of gymnos])erms, 

 the first known forms are as highly specialized as an)- which 

 come later. It is probably safe to say that the conditions of 

 environment may and do act as determinative factors in the 

 evoltxtionary process but they are not the cause of the process. 



The three series of plants may be characterized as folloAvs: 



A. TiiALLOPHYTA. Thallophvtes. GO,()()t) known living species. 



The lowest plants; typically water plants but the majority now with- 

 out chlorophyll and living as parasites or saprophytes in aerial conditions; 

 plant body a thallus, unicellular, coenobioid, or multicellular, usually tila- 

 mentous, very minute to gigantic in size; all gradations from the lowest 

 nonsexual plants to plants with complete se.xuality and often with an 

 alternation of generations but the sporophyte or nonsexual generation 

 always small and not typically deveU)pcd, the gametophyte l)cing the 

 plant; oospherc when present never produced in an archegonium but in a 

 simple oogonium. 



