LIFE HISTORY OF PINUS 3 



CHAPTER V. Fertilization and related phenomena. 

 Conjugation. 



The coming together of the gametophytes 113 



The union of the sexual nuclei 114 



The first division following fecundation. 



The prophases of the division 115 



Later stages in the mitosis 118 



The pro-embryo. 



Division of the two segmentation-nuclei 122 



The four segmentation-nuclei 124 



The development of cell-walls 126 



Later mitoses in the formation of the pro-embryo 127 



The fate within the egg of the smaller sperm-nucleus, the stalk- 

 cell, and the tube-nucleus 128 



Summary 130 



APPENDIX. Some abnormal conditions. 



Supernumerary nuclei in the male gametophyte 133 



Unusual conditions in the female gametophyte 135 



A peculiar method of conjugation 138 



NOTE 139 



LIST OF PAPERS CITED 142 



EXPLANATION OF PLATES 154 



INTRODUCTION. 



THERE is no chapter in the annals of botanical science 

 more fascinating than that which deals with the history of 

 sexuality in plants. No definite date marks the discovery of 

 the fact that plants, like animals, are male and female ; the 

 idea was rather a growth, as is plainly shown by the writings of 

 Aristotle, Theophrastus, Pliny and others of the early philoso- 

 phers. The fact may, however, be said to have been estab- 

 lished by Camerarius (1694) in his " De sexu Plantarum," but 

 for many years after his time botanists found in this question 

 merely a favorite subject for philosophical speculation. Their 

 ideas remained vague and uncertain, no effort being made to 

 confirm their theories either by observation or experimentation. 



It was not until near the middle of the last century that actual 

 investigations were begun along this line. Amici (1830-1846) 

 made certain interesting observations regarding the develop- 

 ment of the pollen-tube and the origin of the embryo in several 

 plants ; but the splendid series of embryological papers pub- 

 lished by Hofmeister (1848-1867) first placed the science upon a 

 sure foundation and marked a new era in the study of sexual 



