THE VASCULAR 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 enor- 

 mously thickened 

 cell - walls, the 

 outer layers of 



which are CUti- 



i j , 



CUlansed , and 



often have a 

 rough and warty 



surface. 



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 



11. Selaginetta spinosa ; megasporangium 

 from same cone in tangential section, mg, 

 megaspores, three out of the four are visible ; 

 *> persistent tapetum ; d, line of dehiscence ; 

 Hq, ligule : L> sporophyll. Magnified about 

 40 diameters. (R. S.) 



