THE HISTORY OF GYMNOSPERMS 203 



primitive stock the other tribes separated later, and the pine tribe itself 

 became more modern. 



The history of Gymnosperms is not complete without mention of its 

 seventh great group, the Gnetales. They comprise three genera, ex- 

 tremely unlike in habit, habitat and geographical distribution, but held 

 together by certain important characters. They are so different from 

 other Gymnosperms that no phylogenetic connection is clear, and there 

 is no sure record of them as fossils. This seems to indicate that they 

 are very modern, but their dissimilarity and their wide separation from 

 one another geographically make it certain that if they are genetically 

 related they must have a history that remains to be discovered. Such 

 suggestions of connection as can be obtained indicate as a possibility 

 that Gnetales are derivatives from the prolific Coniferales stock. 



