PTERYDOPHYTA ; SPERMATOPHYTA 941 



In the Lepidodendrales they were heterosporous, at least in some 

 cases. The cones of Lepidodendron and alhed forms (Lepidostro- 

 bus) vary from an inch to a foot in length, according to species, 

 and are borne on ordinary or on special branches. The sporophylls 

 are arranged spirally upon the axis and each carries a single 

 large sporangium on its upper surface, which in turn carries either 

 an enormous number of minute or a small number of large spores. 

 The upturned and overlapping laminae from the sporophyllae form 

 tlie exterior of the cone. The Lepidodendraceie range from the 

 Devonic to the Permic, while the Sigillariaceas range through the 

 upper Palaeozoic above the Devonic. 



The Ferns are among the most varied of existing pteridophytes 

 and exhibit a wide ran^e in size, from the little epiphytic Hymeno- 

 pltyllacecc, whose fronds are hardly a centimeter in length, to gigan- 

 tic tree-ferns, 80 feet or more in height. The leaves or fronds 

 vary from simple to highly compound, each pinna or pinnule being 

 characterized by a mid-vein, and by forking lateral veins. The 

 sporangia are borne on the under side of the frond, or on separate 

 fronds. In the Ophioglossales a separate spike is produced. In 

 some of the Palaeozoic Cycadofiliccs (comprising most of the ferns 

 of that period *) actual seeds instead of spores were produced, the 

 forms also being intermediate in structure of the stems, etc., be- 

 tween ferns and cycads. The water-ferns or Rhizocarps (Hydro- 

 pteridiales) produce both mega- and micro-spores. The former 

 produce female, the latter male, prothallia. The common pepper- 

 wort, Marsilea, looking like a small four-leaved clover, is a good 

 example. 



Phylum V — Spermatophyta. The true flowering plants 

 (Phanerogams), or seed-plants (Spermatophyta), comprise the 

 gymnosperms and the angiosperms. Conifers are the most abundant 

 representatives of the gymnosperms in the northern regions, while 

 the palm-like cycads occur in tropical districts. They are, however, 

 abundant in the Jurassic and other Mesozoic deposits of America 

 and Europe. The late Palaeozoic Cordaitales were large trees with 

 wood of a coniferous type (Daxoxylen wood) and long strap-shaped 

 leaves. 



The angiosperms, including all the true flowering plants, are 

 divided into the Monocotyledons, which include the grasses, palms, 

 lilies, etc., with parallel-veined leaves, and the Dicotyledons with 

 net-veined leaves. The latter make their first appearance in Co- 

 manchic time. 



* Also classed as a separate order PteridospermcB under the gymnosperms. 



