CONIFERALES 



355 



present time. The accompanying genealogical tree (Fig. 254) 

 will make clear the views as to sequence and affinities developed 

 in the previous paragraphs of the present chapter. The Cordaitales 

 of the Paleozoic serve as the starting-point, and from them were 

 derived two cognate stocks the Coniferales and the Ginkgoales. 

 The latter have suffered much extinction and end in the present 

 epoch in the sole surviving genus, Ginkgo. The Abietineae in 

 earlier Mesozoic time 

 gave rise to the 

 Araucariineae, which 

 flourished greatly in 

 the later epochs of 

 that period, to become 

 almost extinct in the 

 glaciation which 

 ushered in the Ter- 

 tiary. The arauca- 

 rian conifers dis- 

 tinctly took their 

 origin from the 

 abietineous stock 

 after it had developed 

 ligneous resin canals, 

 but before marginal 

 ray-tracheids had 

 made their appearance. The Podocarpineae-Taxineae may have 

 originated at a still earlier epoch and before the abietineous stock 

 had developed the resin canals or the marginal ray-tracheids which 

 distinguish it from the Cretaceous onward. Unlike the Arau- 

 cariineae the Podocarps and their allies, the yews, did not lose the 

 opposite pitting and bars of Sanio common to the parent stock of 

 both Abietineae and Ginkgoales. The Taxodineae are a still later 

 offshoot of the strong abietineous line and come into existence sub- 

 sequent to the appearance of marginal ray-tracheids and ligneous 

 resin canals. Certain conifers of the earlier and later Mesozoic, such 

 as Voltzia, Brachyphyllum, Geinitzia (sometimes erroneously desig- 

 nated Sequoia), etc., which have been referred to taxodineous 



?ora!(7/fa/es 

 FIG. 254. Genealogical tree of the Coniferales, 

 showing their proximity to the Ginkgoales. 



