CHAPTER XXIV 

 THE METAGYMNOSPERMAE: CONIFERALES 



As has been indicated at an earlier stage, the gymnosperms 

 are somewhat clearly divisible into two large groups: the Archi- 

 gymnospermae, which are often fernlike in habit and always 

 cryptogamic in the anatomical organization of their primary 

 wood and in their mode of fertilization by antherozoids, and the 

 Metagymnospermae, which present no external resemblance to 

 the members of the fern series, and in which the centripetal or 

 cryptogamic primary xylem has given place, in living forms at 

 any rate, to transfusion tissue, and in which, also, fertilization 

 by means of a pollen tube is a universal feature. The Coniferales 

 are the largest and the most important group under the Meta- 

 gymnospermae. Their significance from the evolutionary stand- 

 point can scarcely be overestimated, not only because they are 

 more abundantly represented in the living plant population of 

 the earth than are any other gymnosperms, but also because 

 they are copiously preserved as fossils as far back as the Paleozoic 

 age. They thus supply the most important document for the 

 inductive study of general principles of evolution presented by 

 any group of living organisms, vegetable or animal, living or 

 extinct. The paleobotanical and anatomical investigation of 

 the Coniferales has greatly changed our views in regard to their 

 phylogenetic sequence in recent years. The older students of 

 the group restricted to a knowledge of living forms naturally 

 assumed that the conifers, which are the simplest in organization 

 of their vegetative and reproductive parts, are most primitive. 

 By those entertaining this view the Taxineae are considered the 

 most ancient conifers, and with them have been connected, not 

 only the Cordaitales, but also the living genus Ginkgo. In the 

 most recent systematic treatment of the coniferous tribe as a 

 whole we find this attitude maintained, for Ginkgo and Taxus 

 are regarded as closely related. It is needless to state that there 



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