APPENDIX A 



617 



flowers. Instead the seeds are borne on the faces of scalelike leaves 

 (sporophylls), which are generally arranged spirally on an axis so as to 

 form a structure called a cone. The group includes the modern pines, 

 spruces, firs, junipers and yews, 1 sequoias, ginkgoes, and cycads. It also 

 includes various extinct groups, among which are the seed ferns. In struc- 

 ture the members of the Gymnospermae do not differ greatly from the 

 flowering plants. One feature in which they are unlike angiosperms is 

 the usual presence of resin or mucilage ducts in the wood. In the pines 



mgs 



Fig. A. 18. The Carboniferous seed fern Neuropteris. A, reconstruction of the whole plant. 

 B, part of trunk with leaf scars. C, a seed. D, section of unmatured seed, showing the mega- 

 spore (mgs) and husk (h) . (Modified from Turtox chart, courtesy General Biological Supply 

 House, Inc.) 



and their allies, also, the xylem is composed only of tracheids, and the 

 phloem sieve tubes do not have companion cells. All gymnosperms are 

 woody in structure. 



The Gymnospermae fall into two main series — the cycad line, which 

 includes the extinct seed ferns and the cycads; and the conifer line, to 



1 which are assigned the extinct large-leaved evergreen trees, the ginkgoes, 

 the conifers, and a few other aberrant forms. 



The Seed Ferns (Cycadofilicales) were common in the late Paleozoic (Figs. 

 26.11 and A. 18). Most of them were undergrowth plants or small trees, with large 

 1 The cone is often berrylike in the junipers and yews. 



