56 GYMNOSPERMS 



younger than the one shown in fig. 46, have been sectioned, yielding 

 younger stages in both micro- and mcgasf)orangia (fig. 47). 



The microsix)rangia are multilocular. We should hesitate to call 

 them "synangia," since the term implies a fusion of separate sporan- 

 gia to form a single large synangium. The structure, however, is 

 practically identical with that in the Marattiaceous ferns (fig. 48). 

 There is an outer layer of thick-walled cells, followed by thin-walled 



C3> <3 O 



9 C3) C> c^ 

 CB^ (3) O CD CD 



Fig. 50. — Cycadeoidea dacolensis: microspores indicating multicellular structure. — 

 After WiKLAND.**^ 



cells and then, doubtless, a tapetum. There is a cleft between the 

 two rows of loculi, and each loculus opens into the cleft, as in Ma- 

 ratlia. A complete longitudinal section of the sporangium is shown 

 in fig. 49. 



Nothing very definite is known of the internal structure of the 

 microspore, but it seems practically certain that there were several 

 cells. The fact that so many show a circular marking would indicate 

 that there is a prothallial cell (fig. 50). 



No pollen tubes have been observed. There is some nucellar tis- 

 sue, but whether it breaks down so as to allow the pollen grains to 

 come into direct contact with the gametophyte, as in the Cycado- 

 filicales. is not known. 



