334 



GENERAL BOTANY 



gametophyte proper) and of an antheridial cell called the gener- 

 ative cell. The generative cell then divides to form two cells, a 

 stalk cell and a body cell. When the pollen tube forms, the stalk 

 cell disorganizes and frees the body cell, which then divides in the 

 tube to form two male cells (Fig. 198, e). These nonmotile male 

 cells correspond to the motile sperms of the cycads and ferns. 



The female gametophyte is formed within the megaspore by 

 the process of germination, resulting in a- -cellular gametophyte 

 (Fig. 198, a). From three to five archegania are formed on this 



Tube nucleus 



-Stalk cell nucleus 

 \;rMale cells 



^? Pollen tube-'' 



-Pollen grain 



if Micropyle 



Gametophyte 



FIG. 198. Gametophytes and fertilization in the spruce 



o, ovule at the time of fertilization ; b, archegonium with a fertilized egg and male 



(cf) and female (9) pronuclei ; c, d, microspores before and after germination to form 



the gametophyte ; e, pollen tube and male cells, or sperms 



gametophyte at its micropylar end, each archegonium (6) being 

 composed of a large egg cell, a layer of cells called the jacket 

 cells, and the neck cells. Pollination is effected by means of 

 the wind when the young female cones are erect on the ends 

 of the branches. The cone scales are then^open (Fig. 195, 6), and 

 the pollen sifts down "between them and comes to rest in con- 

 tact with the micropyles of the ovules. A sticky secretion is * 

 exuded by the micropyle, as in the cycads, which draws the 

 microspore into the micropyle until it rests on the surface of 

 the megasporangium. No distinct pollen chamber is formed in 

 the spruce, like that in the-cycad megasporangium. The pollen 

 tube begins to grow down into the megasporangium early in 

 May, soon after pollination, and reaches the archegonia late 



