1 84 



MORPHOLOGY 



[eaves or pinnae more or less modified, and may be said to take the fol- 

 lowing forms: (i) epaulet type (Crossotheca), in which the microspo- 



424 



Figs. 423, 424. — Microsporangia of Cycadofilicales, epaulet (Crossotheca) type: 

 423, diagram of cross section, showing the limb (a), the sporangia (b) showing their 

 attachment (d), and the " central boss " (c); 424, diagram of horizontal section, showing 

 the two-chambered sporangia; letters as before. — After Kidston. 



rangia are pendulous from a more or less peltate and stalked lamina 

 (figs. 423, 424); (2) cupule type (Calymmatotheca), in which the micro- 

 sporangia occur in cupule-like structures terminat- 

 ing naked branches (fig. 425); and (3) synangium 

 type, in which the microsporangia occur as synangia 

 upon the abaxial face of fernlike leaves. 



Female gametophyte. — The female gametophyte 

 \ 1 V / is hardly at all preserved, so far as found, and 



\ / sections of the seed give no evidence as to its 



structure. 



Conclusions. — The chief features of this most 

 interesting group may be summarized as follows : 

 It is evidently very closely related to the ferns, 

 the resemblance in external appearance being 

 remarkably close. The vascular anatomy is dis- 

 tinctly of the fern type, but with the additional 

 feature of secondary wood, which is a gymno- 

 sperm feature. The microsporangia are hardly 

 changed from fern sporangia ; but the megaspo- 

 rangia are enormously changed, a well-developed 

 ovule replacing a sorus or a synangium. It seems 

 clear that this, the most ancient group of seed 

 plants, was derived from still more ancient 

 ferns. 



Fig. 425. — Micro- 

 sporangia of Cycado- 

 filicales, cupule (Ca- 

 (ymmatotheca) type; 

 Codonothcca ; sporangia 

 on the inner surface of 

 the cupule valves. — 

 After Sellards. 



