S5o STUDIES IN FOSSIL BOTANY 



preservation, no embryo has, as yet, been found in any 

 of them. The possible explanation of this fact has 

 been discussed in connection with the seed of Lygino- 

 dendron (see Chap. X. p. 393). 



The investigation of the Palaeozoic seeds, which 

 was allowed to rest for some time after the classical 

 researches of Brongniart, Renault, and Williamson, is 

 now again being actively pursued, having been greatly 

 stimulated by the discovery of the seeds of the 

 Pteridosperms. 



7. Affinities. — We have now completed our sketch 

 of the principal characters of the Cordaiteae, and may 

 briefly sum up the conclusions to which we are led. 



In their vegetative characters, the Cordaiteae hold 

 the balance very evenly between Cycads and Conifers, 

 while at the same time showing much that is peculiar 

 to themselves. The structure of stem and root is, 

 on the whole, very near that of the Coniferae ; the 

 secondary wood especially would by itself rouse no 

 suspicions that we had anything but an Araucarian 

 Conifer before us. The large size of the pith in the 

 stem, however, is unlike anything known in Coniferae, 

 and rather suggestive of a Cycad, though in its peculiar 

 discoid structure the pith of some Cordaiteae is quite 

 different from that of Cycads. 



The double leaf-trace is a striking point of agree- 

 ment with Ginkgo on the one hand, and with certain 

 of the Pteridosperms on the other ; Poroxyleae form 

 a connecting link with the latter in this respect. 



The wood of the stem was wholly centrifugal in 

 development, in many of the specimens investigated 



