512 



General Botany 



Figs. 318 and 319. At the left, staminate cones of Pinus rigida clustered about the 

 bases of the new shoots. At the right, one-, two-, and three-year-old cones of Pinus pungens. 



cropyle. Within the nucellus four megaspores are formed. 

 Three of these degenerate as the fourth enlarges. The production 

 of the megaspore ends the sporophyte generation. 



The megaspore germinates the following spring and forms 

 within the nucellus a mass of tissue, the female gametophyte, 

 at the expense of the food contained in the surrounding cells. 

 The female gametophyte grows during the spring and by June 

 has organized several archegonia just beneath the micropyle. 

 Each archegonium consists of a large egg cell and several very 

 small neck cells. 



Pollination. At the time the pollen is shed the axis of the 

 ovulate cone elongates, separating the sporophylls. Some of the 

 pollen grains drift in between the sporophylls and become 

 lodged near the micropyle. These are filled with a sticky fluid 

 at the time, and the pollen grains adhere to it. As the fluid sub- 

 sequently dries, the pollen grains are drawn within the micropyle. 



Pollination occurs in May or June, about the same time that 

 the megaspore is being organized within the nucellus. The 



