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. 



B 



FIG. 300. "The gametophytes of the pine 



, 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 

 nj pc, pollen chamber; m, micropyle; i, integument. Z>, germinating pollen 

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

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

 s, the two sperm nuclei. 7), 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. /?, C', 

 after Miss Ferguson 



