CHAPTER II 



THE DEVELOPMENT OP SEX IN PLANTS AND A STUDY 

 IN EVOLUTION 



So far we have confined our attention to the study of 

 life-forms which, multiply asexually. It will be inter- 

 esting, in the present chapter, to consider, at least in 

 part, the beginnings of sex in plants, and to trace it 

 from its simplest manifestation through some stages 

 of its development. 



We shall begin with those wonderful, microscopic, 

 one-ceU plants familiar to even the most amateur 

 microscopist as Diatoms (Grr. dia, through; temnein, to 

 cut). They occur in vast numbers and extraordinary 

 variety in both salt and fresh water, on damp soil, 

 among moss, in the drifting plankton of lakes and seas, 

 on the surface of the mud of ponds and pools, on wet 

 stones and rocks, attached to aquatic plants and decay- 

 ing vegetation. Many forms are solitary, others exist 

 in colonies; some float freely, others attach themselves 

 to an anchorage by means of gelatinous stalks. The 

 cells in some instances form zigzag chains or bands. 

 The form of the cells varies most remarkably; it may be 

 rodlike, circular, oval, wedge-shaped, or curved. The 

 protoplasmic cell contains a single central nucleus and 

 colour-bearing bodies called " chromatophores," which 

 may be few or many. These chromatophores are tinged 



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