438 GYMNOSPERMS 



carioxylon type of wood ; but this wood probably belonged to the 

 Cordaitales. The "parallel'' veined leaves of Cordaitales once placed 

 the monocotyls in the Carboniferous, and settled "by the sure 

 testimony of history" that the monocots must be older than the 

 dicots. However, the mere fact that the wood structure is so similar 

 in the two cases should have some weight. Scott believed that the 

 Araucariaceae have the longest fossil history of any of the Conifer- 

 ales, overlapping that of the Cordaitales. Consequently, they 

 might have come from the Cordaitales. 



Material is being found farther and farther back, and claims are 

 being made that both Abietaceae and Araucariaceae existed in the 

 Permian. 



The Taxodiaceae and Cupressaceae have not occasioned so much 

 discussion, probably because it is rather generally agreed that they 

 are a branch from the general abietineous stock. Their fossil record 

 does not go as far back. They were abundant in the Cretaceous, 

 and such names as Cuprcssites, Widdringtonites, and Thujitcs in- 

 dicate their resemblance to living genera. Cupressuioxylon is Juras- 

 sic, and the family doubtless was more widely represented in that 

 time, but material has not been identified with as much confidence. 

 When Florin completes his work on cuticular structures, some of 

 the material which has been identified tentatively may be assigned 

 definitely to its proper place. 



Both families have the ligneous resin canals and the marginal ray 

 tracheids which characterize the Mesozoic Abietaceae. In tracing 

 the origin of the two families, evidence from the Mesozoic Sequoias 

 should be left out, for they are more like the Araucariaceae, and may 

 belong with them. 



In gametophytic characters the two families illustrate how one 

 feature may advance while another retains its primitive character. 

 In Juniperus, and in the Cupressaceae generally, there is no pro- 

 thallial cell in the male gametophyte. In the pollen tube there are two 

 male cells, which have progressed but little beyond the swimming 

 sperm level. But in the female gametophyte, there is no wall be- 

 tween the ventral canal nucleus and that of the egg. Such features 

 should be considered along with the evidence from comparative 

 anatomy. 



