PINUS AUSTRIACA, OR P. LARICIO. 139 



6. The opening, the micropyle. 



c. The tissue enclosed by the integument, the nucellus. 



d. Within the nucellus the large rounded cell, the mega- 

 spore, or the embryo-sac containing female gametophyte. 1 



In fully developed female gametophytes observe: 



e. Their general form at their micropylar ends. 



/. The archegonia. Study the archegonia in detail, ob- 

 serving: 

 i. The large base the egg and the prominent nucleus 



it contains, 

 ii. The neck opening toward the micropyle. 



g. In some cases may be seen pollen-grains that have been 

 deposited on the nucellus, and from which pollen-tubes 

 have grown toward the necks of the archegonia for the 

 purpose of carrying the male cells to the egg. 2 Ob- 

 serve especially the tortuous course of the pollen-tube. 



h. In older ovules the young embryo of the sporophyle 

 may be seen. Note its form and structure; also how 

 it has used up adjacent gametophyte tissue as food. 



i. From fully developed ovules (seeds') dissect out the 

 embryo and note root, stem, and cotyledons (seed-leaves), 

 noting also how completely it is surrounded by the 

 female gametophyte tissue. Identify in the seed the 

 various parts of the ovule. 



/. Observe the wing on fully ripened seeds. Drop one from 

 a height of a few feet, and time its fall. Then tear away 



1 In most cases the student will find no megaspore within the sporan- 

 gium, since the megaspore will have germinated to produce the embryo- 

 sac and female gametophyte. These are enclosed by the nucellar 

 tissue. In prepared sections they are often so contracted as to be 

 pulled away from the surrounding nucellar tissue. 



2 Since the male gametophyte and male cells are at first entirely enclosed 

 by the wall of the former microspore, in order to bring the male cells 

 into the vicinity of the female gamete (egg), the entire microspore with 

 its contents is carried by the wind to the nucellus of the sporangium. 

 This transfer of microspores is called pollination. When the spore is 

 located on the nucellus the processes of fertilization may begin. 



