THE REPRODUCTIVE STRUCTURES 103 



cells called the "tapetum." The interior is occupied by 

 the spores. 



Throughout the plant kingdom the male structures 

 are far more conservative than the female, so that the 

 microsporangium of the cycads is only an illustration of 

 a general phenomenon. The megaspore never escapes 



50 51 



Figs. 50-51. — A comparison of the sporangia of a cycad and a fern 

 resembling the ferns of the carboniferous: Fig. 50, longitudinal section 

 of microsporangium of Dioon edule, with numerous spores; Fig. 51, 

 similar section of a sporangium of Angiopleris. 



from the megasporangium, but the microspore is shed, 

 as in its remote fern ancestors. Other features which the 

 male structures of cycads have persistently retained 

 have been mentioned in the preceding paragraphs. 



THE MALE GAMETOPHYTE 



The microspore is the first cell of the male gameto- 

 phyte, but leading up to its formation there is a series of 



