372 



THE SPERMATOPHYTES 





Meanwhile the scales of the cone close together and the cone 

 bends over until it hangs downward. This is a curious behavior, '' 

 although there is evident advantage to the plant, for the cone is now 

 in a better position to protect the ovules from rain or dust which 

 might enter between the scales if the cones remained upright. 



FIG. 300. The gametophytes of the pine 



A, diagram of a section of a year-old ovule: embryo sac with mature archegonia 

 ar imbedded in the tissue of the endosperm (female gametophyte) ; pollen 

 tubes (male gametophytes) growing down through the tissue of the nucellus 

 n; pc, pollen chamber; m, micropyle; i, integument. B, germinating pollen 

 grain, showing young male gametophyte : t, tube nucleus ; g, generative nucleus ; 

 p, prothallial cell. C, tip of pollen tube applied to the egg: t, tube nucleus; 

 s, the two sperm nuclei. D, a mature archegonium sunken in the tissue of the 

 endosperm, showing the large egg surrounded by a jacket of cells rich in proto- 

 plasm: two neck cells of the archegonium shown just above the egg. B, C, 

 after Miss Ferguson 



