368 



GAMETOPHYTE OF FINALES 



of the nucleus of the megaspore, the gametophytic tissue being 

 developed at a later period. You have noticed that there is no 

 chamber formed above the archegonia, and it would be a natural 

 inference that the male gametophyte must be of a somewhat 

 different character from that of the cycads in order to met this 



mc 



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

 bearing two sporangia. B, section of A, taken through one of the sporangia, 

 showing a small bract, s, and large scale-like outgrowth which bears the 

 sporangia, sp. The sporangium is surrounded by an integument, i, and con- 

 tains 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 gamet- 

 ophyte, showing two archegonia with large female gametes, 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; t shows the disorganization caused by 

 the tube cells as they grow towards the archegonia. 



