33& 



GAMETOPHYTE OF PINE 



the micropyle, or the microspores may be drawn through the mi- 

 cropyle by mucilaginous excretions as in the cycads. The early 

 stages in the germination of the microspore are essentially as in 

 Cycas, though more reduced. The microspore on reaching the 



roc 



Fig. 253. Megasporangia of pine : A, scale-like outgrowth of sporophyll 

 hearing two sporangia. B, section of A, taken through one of the spo- 

 rangia, showing the sporophyll, s, and large scale-like outgrowth which 

 bears the sporangia, sp. The sporangium is surrounded by an integument, 

 i, and contains a single megaspore, m, as in the Cycads. mc, microspores 

 that have been drawn through the micropyle to the sporangium, into which 

 their tube cells are growing. C, section of megasporangium enlarged and 

 diagrammatic, showing the female gametophyte at the time of fertilization 

 — g, female gametophyte, showing two archegonia with large female ga- 

 metes, fg. At the left the tube of the microspore, mc, has entered the neck 

 of the archegonium and the two male gametes have been discharged into 

 the large sac of the female gamete. On the right the tube cell with male 

 gametes is seen approaching the neck of the archegonium. i, integument ; 

 sp, remains of sporangium not disorganized by the gametophyte; / shows 

 the disorganization caused by the tube cells as they branch and grow 

 towards the archegonia. 



