SPERMATOPHYTES 



205 



bears one or two bractlets and d terminal ovule (fig. 463). The bearing 

 of ovules on secondary axes of the strobilus results in what is called a 

 compound strobilus, a type of strobilus characteristic of certain conifers. 



Ovules. Although the 

 structure of the testa is not 

 clear in the sections that have 

 been made (fig. 463), two 

 layers are evident (the outer 

 fleshy and the stony), and it 

 is probable that an inner 

 fleshy layer was also present. 

 This type of testa is char- 

 acteristic of the whole cycad 

 line of gymnosperms. An- 

 other primitive feature of the 

 ovule is that the nucellus is 

 quite free from the integu- 

 ment, and that one of the 

 sets of vascular strands trav- 

 erses the outer fleshy layer, 

 and the other set traverses 

 the peripheral region of the 

 nucellus. This structure is 

 duplicated only among the 

 Cycadofilicales. There is also 

 a prominent nucellar beak 

 and a large pollen chamber, a 

 structure which indicates the 

 existence of swimming sperms. 



Male gametophyte. The 

 pollen grains are preserved in 

 abundance, and in favorable 

 specimens a group of internal 

 cells is evident (fig. 464), 



which must represent a male gametophyte; but whether these cells are 

 vegetative or spermatogenous or both cannot be determined. In either 

 case, the number of cells indicates a Yery primitive condition. 



Female gametophyte. The female gametophytes resemble those of 

 modern gymnosperms. Two archegonia have been seen, and between 



FIG. 462. Section of staminate strobilus of 

 one of the Cordaitales, showing the spirally ar- 

 ranged sterile bracts, and the stalked stamens 

 bearing terminal sporangia (the longitudinal de- 

 hiscence of the sporangia not shown). After 

 RENAULT. 



