1 86 MORPHOLOGY AND LIFE HISTORY 



within the embryo-sac, and enlarged by growth, forms 

 the young female gametophyte (endosperm). The 

 megasporangium, surrounding the endosperm, is called 

 the nucellus, as in Zamia, and both these structures are 

 surrounded by a protecting envelope, the integument. 

 The pollen-chamber lies between the tip of the nucellus 

 and the integument. The micropyle leads through 

 the integument to the pollen-chamber. In the pol- 

 lination of Pinus the entire pollen-grain passes into 

 the pollen-chamber through the micropyle. 



L. The Ovule: 



The endosperm, nucellus, and integument together 

 form the young ovule. Nearly one year is required 

 for its development to the stage described above. In 

 the second spring, while the pollen-tube is rapidly 

 elongating, and the nuclear divisions noted above are 

 taking place within it, several archegonia develop in 

 the micropylar end of the endosperm. In the venter 

 of each archegonium lies the large egg. 



M. Fertilization: 



Eventually the pollen-tube enters the neck of an arche- 

 gonium (compare with the process in- Zamia and other 

 Cycads), its contents are discharged into the venter, 

 and one of the sperm-nuclei fuses with the nucleus of 

 the egg. Thus fertilization is accomplished, about one 

 year after pollination. The transfer of the sperm- 

 nucleus to the egg by means of a pollen-tube is called 

 siphonogamy, and plants in which this occurs, 

 Siphonogamia. 



The one-year-old cone, to be studied next, represents 

 the stage of development at about the time of fertiliza- 

 tion. The sperms of Pinus are non-motile. 



N. The One-year-old Car peltate Cone: 



i . Compare the position on the branch, and the atti- 



