78 



MORPHOLOGY OF GYMNOSPERMS 



whole cycadophyte phylum, including even the Cycadales, and is 



one of its striking features. 



THE MEGASPORANGIUM 



If the microsporangiate structures of Bennettitales have advanced 

 little beyond the fern level, no such claim can be made for the mega- 



sporangiate structures. They are not only 

 remarkably different from the corre- 

 sponding structures among Cycadofilicales, 

 but they are even more different from those 

 of the Cycadales. 



The description of Bennettites Gih- 

 sonianiis, as given by Carruthers (2), 

 Solms-Laubach (5, 6), and Scott (10), 

 may be used as an introduction to the 

 situation (fig. 63). From the convex 

 surface of the hemispherical receptacle a 

 great number of slender stalks arise, which 

 pass vertically upward, or diverge slightly 

 toward the curved surface of the " fruit." 

 The central stalks are the longest, the 

 outer ones gradually diminishing in length, 

 so that the general outline is oblong or 

 obovate. Each of these stalks bears at 

 its tip a single erect seed, with the micro- 

 pyle directed outward. The seeds are so 

 placed that the long axis meets the sur- 

 face approximately at right angles. The 

 spaces among the stalks are packed with 

 scales, which are dilated at tip, between 

 the seeds, so as to form a continuous en- 

 velope, interrupted only by the small pits 

 through which the micropylar tubes project. 

 The corresponding structures of the beautifully preserved Cycade- 

 oidea Wielandii (fig. 64) have been more fully described by Wieland 

 (22). They conform to the description of Bennettites given above, 

 but many additional details are given. In the lower part of the ovulif- 



FiG. 62. — Cycadeoidea da- 

 cotensis: longitudinal section 

 of synangium, showing stalk, 

 hard outer layer of cells, por- 

 tions of wall layers of cells, 

 and two chambers containing 

 pollen grains; X40. — -\fter 

 Wieland (22). 



