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. 



; % 



-n M\mr&?- y - *J 



(* Endosperm {; 







FIG. 300. The gametophytes of the pine 



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

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

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

 n ; p c, pollen chamber; m, micropyle ; i, integument. B, 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. 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. /*, C', 

 after Miss Ferguson 



