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APPENDIX A 



The horsetails were formerly much more important than they are today. In 

 Paleozoic times (Devonian to Permian, and especially in the Carboniferous) there 

 lived a great variety of treelike plants of this group, belonging to the order 

 *Calamitales and the genus *Calamites. Some of these are shown in Figs. 26.12 

 and 27.20, and their structure and mode of reproduction are indicated in Fig. A. 14. 

 They attained a height of 60 and sometimes 90 feet, with a diameter up to 15 

 inches. The stem had a thick bark and a ring of xylem enclosing a large central 

 pith. It was abundantly branched, with a crowded tuft of leaf whorls at the apex 

 of the main stem and at the nodes of the branches. Calamites differed chiefly from 



its small modern relatives in its much 

 larger size and in the fact that its stems 

 showed secondary thickening. 



A third order, *Sphenophyllales, 

 included many small herbaceous or 

 vinelike undergrowth plants in the coal 

 forests of Carboniferous time; the 

 whorled leaves were wedge-shaped. 

 *Sphenophyllum appears in Fig. 27.20. 



Subphylum III. Lycopsida (H 

 cop' si da). 



The Club Mosses and Their Allies. 

 Like the last, this suborder also 

 contains but a single class, the 

 Lycopodinae, better represented in 

 the past than today. One of the 

 four orders, the *Lepidodendrales, 

 is extinct; the other three have 

 living representatives. 



Fig. A. 13. The common field horsetail or 

 scouring rush, Equisetum arvense. A, the 

 sterile sporophyte plant. B, a spore-bearing 

 shoot. C, sporangia in a conelike structure 

 at the shoot tip. {Courtesy General Biological 

 Supply House, Inc.) 



The best-known group includes the ground pines, running pines, or club mosses, 

 of the order Lycopodiales. Most of these belong to the largest of the two surviving 

 genera, Lycopodium, which has about 300 species. They have a sprawling stem 

 with erect branches, all parts of the stem and branches being covered with small, 

 generally sharp-pointed leaves. The spores are produced in sporangia borne by 

 sporophylls that may be distributed along the branches or grouped into conelike 

 apical structures. All the spores are alike, each capable of producing a minute 

 but generally free-living gametophyte that bears both antheridia and archegonia, 

 as in most other primitive vascular plants. 



Selaginella (order Selaginellales) is a genus of about 600 species, some of which 

 are called little club mosses (Fig. A. 15). It includes plants similar to but more 

 delicate than Lycopodium; many of them grow in moist tropical forests, but a 

 few live in very dry places. The resurrection plant of the southwestern United 

 States and Mexico is a xerophytic Selaginella, which can dry and curl up into a 

 ball and lie dormant for months until the return of moist conditions. 



