DEVELOPMENT OF PLANTS 



353 



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 



jnc 



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

 bearing two sporangia B, section of .4, taken through one of the sporangia, 

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

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

 tains a single megaspore, w, 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. 



24 



