CHAPTER XXIII 



THE ARCHIGYMNOSPERMAE: CORDAITALES 

 AND GINKGOALES 



The two tribes of gymnosperms discussed in the present chapter 

 no longer possess the fernlike habit of the Archigymnospermae 

 which have just been considered, but still maintain the pollen 

 chamber and the cryptogamic wood so characteristic of the Cyca- 

 dofilicales and Cycadales. Of the two groups here discussed the 

 Cordaitales became entirely extinct at the end of the Paleozoic 

 or at the beginning of the Mesozoic and have a geological range 

 extending far into the past. On the other hand, the Ginkgoales, 

 although present somewhat doubtfully in the Paleozoic, had their 

 greatest development in the Mesozoic and persist at the present 

 time in a monotypic genus of Eastern Asia. 



The Cordaitales were freely branched trees resembling in 

 general habit our existing conifers, to which they are usually 

 considered to have given origin. The trunks often reached a 

 considerable size, and the woody cylinder included a large pith, 

 in some instances septate and occupied by air spaces, which, 

 however, unlike the medullary fistulae of Catamites, were much 

 more numerous than the internodes. The cavernous character 

 of the pith as well as its large size is responsible for the existence 

 of medullary casts in the case of the Cordaitales, and these are 

 assembled under the form-genus Artisia or Sternbergia. The 

 surface of the stem was often provided with the sclerenchymatous 

 armor which has been noted as a feature of organization of the 

 axes of the Cycadofilicales. Fig. 216 illustrates the general 

 topography of a segment of the stem in a cordaitean form. The 

 woody cylinder was without annual rings, except in the later 

 Paleozoic and hi higher latitudes. This situation is very well 

 shown by Figs. 217 and 218, illustrating the structure of cordaitean 

 woods from Northern England (Lancashire) and Southern Canada 

 (Prince Edward Island). In the first specimen annual increments 

 can be somewhat clearly distinguished, while in the second they 



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