Cnapter 3 



THE EVOLUTION OF PLANT 

 REPRODUCTION 



As plant bodies evolved from the unicellular condition to the 

 large and complex forms of trees and other flowering plants, 

 division of labor resulted not only in the localization of various 

 maintenance functions in special organs such as roots, stems and 

 leaves; but also in a segregation of reproductive abilities in 

 definite portions of the plant. In place of the primitive condition 

 whereby any part of the plant could reproduce the entire 

 organism, special cells, tissues and organs were set aside for re- 

 productive purposes. This restriction of reproductive powers 

 has its culmination in such complex structures as flowers, seeds 

 and fruits. 



The numerous types of reproduction found in the plant 

 kingdom are but variations of the two basic methods of asexual 

 and sexual reproduction described in the first chapter. The 

 asexual method was undoubtedly the first to appear, and from it 

 evolved primitive sexual types of reproduction as well as the more 

 complex asexual and sexual habits of land plants. As in the study 

 of the maintenance activities of plants, it will be convenient to 

 limit our attention to a few significant types which are represent- 

 ative of the important stages in the evolution of plant reproduc- 

 tion. These include (7) reproduction in unicellular plants, (2) 

 reproduction in multicellular thallus plants, (3) the reproductive 

 cycle of a moss, (4) the reproductive cycle of a fern, (5) the repro- 

 ductive cycle in the little club moss, (6) the reproductive life 

 history of a Gymnosperm, or cone-bearing seed plant, and (7) the 

 reproductive life history of an Angiosperm, or flowering seed 

 plant. 



In such a series there is evident an increasing adaptation of 

 plant reproduction to conditions of terrestrial life, especially in 



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