THE VASCULAK CRYPTOGAMS 



19 



The one favoured mother-cell divides into four tetra- 

 hedrally arranged daughter - cells ; each daughter - cell 

 becomes a megaspore. The four megaspores develop 

 enormously, and gradually displace and absorb all the 

 remaining mother-cells, which, however, can be seen for 

 a long time lying inert in the sporangial cavity. The 

 four megaspores, 

 as they grow, 

 gradually take 

 possession of the 

 whole interior of 

 the sporangium, 

 which itself grows 

 to a greater size 

 than the micro- 

 sporangium (see 

 Figs. 4 and 11). 

 The megaspores 

 acquire greatly 

 thickened cell- 

 walls, the outer 

 layers of which 

 are cuticular- 

 ised, and often 

 have a rough 

 and warty sur- 

 face. 



FIG. 11. Sdaginclla spinosa ; megasporangium 

 from same cone in tangential section (trans- 

 verse to sporophyll) ; mg, megaspores, three out 

 of the four are visible ; t, persistent tapetum ; 

 d, line of dehiscence ; lig, ligule ; L, sporo- 

 phyll. Magnified about 40 diameters. (R. S. ) 



We see then that a megasporangium differs from a 

 microsporangium in the fact that only one mother-cell 

 divides, and that its daughter-cells occupy the whole 

 sporangium, which thus contains four spores only. 



The megaspores, the diameter of which is about 

 twenty times that of the microspores, attain their 



