FECUNDATION IN PLANTS. 



CHAPTER I. INTRODUCTION. 



The processes of nuclear division and cell-formation are so closely 

 associated with sexual cells and their development that an adequate 

 understanding of these cells is impossible without a definite and 

 thorough knowledge of the processes involved in their development. 

 Our interpretations of the significance of the sexual process and the 

 phenomena of heredity in all organisms will be more lasting and help- 

 ful as scientific knowledge if these interpretations or doctrines are 

 based upon a well-connected phylogenetic series of the most funda- 

 mental facts. Perhaps no other field of research has been more 

 helpful during the past quarter of a century in enabling the biologist 

 to gain a deeper and more far-reaching knowledge of the physical 

 basis of heredity than the study of mitosis, especially in reproductive 

 cells. The division of the nucleus naturally suggests the division of 

 the cell, or the process by which new cells are formed from a mother- 

 cell, and the study of cell-formation in very recent years, especially 

 among the lower plants, has not only wrought almost a revolution 

 in our knowledge of the processes here involved, but has also furnished 

 new criteria for determining relationships and probable lines of descent. 



It is deemed necessary, therefore, to introduce the subject of sexual 

 reproduction in plants by a brief presentation of the typical processes 

 of nuclear and cell-division in both the lower and higher forms. In 

 doing so these processes will be described in a few of those forms 

 which have been subjected to a critical study by means of the most 

 improved methods and instruments. The processes described will be 

 confined largely, though not exclusively, to spore mother-cells. 



The division of the nucleus and of the cell presents generally three 

 processes, the development of the karyokinetic spindle, the behavior 

 of the chromatin, and the formation of the cell-plate or new plasma 

 membrane. This division is made merely for the sake of convenience, 

 as it is not implied that three distinct or separate processes are 

 necessarily involved, although the development of the plasma mem- 

 brane in many cases has apparently little or no connection with the 



