314 



PLANT MORPHOLOGY 



were not produced. Remains of the female gametophyte are fragmen- 

 tary, but it is certain that archegonia were developed in the micropylar 

 region of the nucellus, the microspores apparently coming directly in con- 

 tact with them. No embryos have ever been found in the seeds, perhaps 

 because they did not develop until after the seeds had been shed. 



Fig. 262. Diagrammatic longitudinal section of the ovule of Lyginopteris oldhamia 

 {Lagenostoma lomaxii) with its investing cupule; n, central portion of nucellus; n', outer 

 hardened portion with the pollen chamber between; i, inner fleshy layer of integument; 

 h, vascular bundle; s, outer stony layer of integument; c, cupule. {After Oliver.) 



Summary. The Cycadofilicales are a group that was dominant in the 

 Paleozoic. It is closely related to the Filicinae, the general habit, leaves, 

 and microsporangiate structures being distinctly fern-like. The vascular 

 anatomy is also fern-like, but with the addition of secondary wood. 

 Three stelar types are represented. A primitive feature is the occurrence 

 of mesarch xylem throughout the plant, an advanced feature, the presence 

 of pitted tracheids. There is no strobilus and the sporophylls are leaf-like 

 and not highly differentiated from foliage leaves. The microsporangia 

 resemble fern sporangia in being numerous on the sporophylls, but the 

 megasporangia, in forming seeds, show a great advance. The Cycadofili- 

 cales are transitional between the ferns and cycads. They were probably 

 ancestral to both the Bennettitales and Cycadales. 



