SPERMATOPHYTA 



55 



ORDER d, SPHENOPHYLLALES 



A Paleozoic group of slender plants with jointed stems, and 

 leaves in \yhorls. They were probably trailing or climbing in 

 habit, and are known from the Devonian to 

 the Permian. 



Sphenophyllum and a related Mississippian 

 genus, Cheirostrobus, based on one of the most 

 beautifully preserved fossil fruits ever recovered, 

 combine to such a degree the characters of both 

 the lycopods and the equisetes that the Spheno- 

 phyllales are held to be the descendants of the 

 ancient stock from which club-mosses and 

 horsetails have diverged in the course of evolu- 

 tion. The group became extinct at the close 

 of the Carboniferous. 



Sphenophyllum (Fig. 17). — A small, branch- 

 ing plant with slender, ribbed stems, represented 

 by many species in the Pennsylvanian coal 

 fields of eastern North America. Leaves 

 usually six in a whorl and wedge shaped or cut 

 into lobes. Thus externally it resembles a 

 small Calamites, but the anatomy of the stem, 

 and of the cone, show it to be different. The name from the 

 Greek sphenos, a w^dge, + phyllon, a leaf, refers to the usual 

 shape of the leaves. 



Fig. 17. — Spheno- 

 phyllum schlot- 

 heimii Brongni- 

 art, from the 

 Pennsylvanian 

 coal deposits of 

 Pennsylvania. 

 Natural size. 

 (Redrawn from 

 Lesquereux.) 



1. Has this order any living representatives? 



2. Describe Sphenophyllum. 



3. How is this order related to the club-mosses and the horse- 

 tails ? 



DIVISION IV, SPERMATOPHYTA 



These include the most highly organized plants and are dis- 

 tinguished by the production of seeds (whence the common 

 name of seed-plants). The difference between these and the 



