Revisions of Some Plant Phyla 3 r 



sporophylls which occur in strobiH, the microspores set free in 

 germination producing tubular antherids ; the megaspores re- 

 tained in their sporangia, where they develop gametophytes and 

 archegones ; after fecundation of the egg by the motile sperms, 

 the embryo sporophyte surrounded by the gametophyte tissue 

 embedded in the i- or 2-coated sporangium constitutes the 

 " seed." (Living species about 140, but very many extinct.) 



Class 2y. PTERIDOSPERMEAE ( Cycadofilices) . Seed Ferns. 

 Palaeozoic plants, long extinct, related to the ferns on the one 

 hand, and the following classes on the other. Stems short and 

 erect, increasing in thickness, bearing pinnate leaves. 



Order Pteridospermales. With the characters of the class. 



Family i. Lyginopterideae. With stems which seem to have 

 had the power of increasing in diameter by the growth of their 

 collateral bundles. Lyginopteris, Megaloxylon, Calamopitxs. 

 (Pf. I, 4, 783.) 



Family 2. Medulloseae, related to the preceding. Medullosa, 

 Steloxylon. (Pf. I, 4, 788.) 



Family 3. Cladoxyleae, including Cladoxylon and Voelkelia. 

 (Pf. I, 4, 782.) 



Family 4. Protopityeae, mcXw^mg Protopitys. (Pf. 1,4, 794.) 

 Family 5. Araucarioxyleae, including Araucarioxylon. (Pf. 

 I, A, 795-) 



Class 28. CYCADIXEAE. Common Cycads. Plants with 

 erect, woody, little-branched stems, bearing terminal clusters of 

 pinnate leaves. The collateral fibrovascular bundles are arranged 

 concentrically in the stem; these increase the thickness of the 

 stem by development of their cambium, and also by the formation 

 of new bundles in the cortical meristem. Sporophylls in dioecious 

 strobili. ]\Iany cyads which existed in Mesozoic times have be- 

 come extinct, leaving only a few genera and species in the present. 



Order Cycadales. With the characters of the class. 



Family 6. Cycadaceae. Tropical trees of the present time pro- 



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