A Synopsis of Plant Phyla 47 



Family 4. Lepidodendraceae. Leaf-scars large, rhomboidal, 

 crowded together. Lcpidodcndron, Lcpidoplilois. ( Pf. I, 4, 



7^7-) 



Family 5. Bothrodendraceae. Leaf-scars small, ovate, widely 

 separated. Bothrodcndron. (Pf. I, 4, 739.) 



Family 6. Sigillariaceae. Leaf-scars medium-sized, ovate- 

 angled, less widely separated, but not in contact. Sigillaria. ( Pf . 



I. 4. 740.) 



Family 7. Pleuromoiaceae. Leaf-scars n:edium-sized, regu- 

 larly ovate, or much elongated, less widely separated, but not in 

 contact. Plcurouioia. (Pf. I, 4, 754.) 



Phylum Xn. CYCADOPHYTA. The Cycads. 



Chlorophyll-green terrestrial plants in which the alternation of 

 generations is obscured by the reduction of the gametophyte to a 

 condition of dependence upon the long-lived, leafy-stemmed 

 sporophyte. Spores of two kinds (heterosporous), borne on 

 sporophylls which occur in strobili, the microspores set free, the 

 megaspores retained in their sporangia, where they develop gam- 

 etophytes and archegones ; after fecundation of the egg by the 

 motile spermatozoids, the embryo sporophyte surrounded by the 

 gametophyte tissue embedded in the i- or 2-coated sporangium 

 constitutes the "seed." 



Class 27. CYCADOFILICES (Pfcridospcnncac). 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. 



Family i. Lyginopterideae. With stems which seem to have 

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

 collateral bundles. Lyginoptcris, Mcgalo.v\lon, Calaniopifvs. 



(Pf. L4. 783-) 



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

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



Familv 3. Cladoxyleae, including Cladoxylon and J'oclkclia. 

 (Pf. I, 4, 782.) 



321 



