428 



STRUCTURE AND LIFE HISTORIES 



st.c 



contents of the nucellar tissue, thus facilitating the 

 passage of the delicate tube. The dissolved con- 

 tents nourish the growing tube, which at first serves 

 as a haustorium to absorb the 

 nourishment. Thus the male (as 

 well as the female) gametophyte, 

 lives as a parasite upon the tissue 

 of the sporophyte. 



Soon after the pollen-tube has 

 begun to form, the tube-nucleus 

 moves down toward the tip, 

 where it remains, presiding over 

 the subsequent growth of the tube 

 (Fig. 318). At about this time, 

 also, the antheridial mother-cell 

 divides, forming a wall-cell 1 and 

 a generative cell. In this condi- 

 tion the first winter is passed. 

 After pollination the carpellate 

 scales, by growth, are brought 

 close together, and secrete a very 



FIG. 318. White pine . J 



(Pinus Strobus). Germi- sticky, resinous substance, all of 



very completely excludes 



g.c, generative cell; t.n, any water from between the scales. 



tube-nucleus. X about ,_, , 



236. (After Margaret C. The cone then increases greatly in 



Ferguson.) ^ size ( Fjg . ^^ 



381. Fertilization. Early in the following spring (May- 

 June), the generative cell, after passing into the pollen- 

 tube, divides to form two sperm-cells, and the pollen-tube 

 continues its growth toward the archegonia. By this 

 time (June) the egg lies mature within, and completely 



1 Also commonly -called "stalk-cell." 



