CHAPTER VI 

 COMPARATIVE MORPHOLOGY OF GYMNOSPERMS 



Aftee having considered the details of structure presented 

 hj the living and extinct groups of Gymnosperms, it will be 

 well to summarize them, and to obtain some conception of Gym- 

 nosperms as a single well-defined assemblage of forms. In this 

 way the contrasting characters of the different groups may be 

 emphasized, and the relations of Gymnosperms to Pteridophytes 

 on the one hand, and to Angiosperms on the other, may be made 

 to stand out more sharply. 



I. THE VEGETATIVE ORGANS 



THE STEM 



.Ml known Gymnosperms are woody plants, almost all being 

 trees. Whether the group ever contained herbaceous members 

 or not is an interesting but an unanswerable question. The 

 short tuberous stems of many Cycads, of Bennettitales, and of 

 Tumboa; the simple, palmlike column of certain Cycads; the 

 tall trunk of the Cordaitales, branching only above ; the excur- 

 rent shaft of most of the Conifers and of Ginkgo with its sym- 

 metrical monopodial branching; the trailing and spreading 

 habit of certain Conifers; the straggling shrubby habit of 

 Ephedra; and the high climbing habit of certain species of 

 Gnetum, is a list which seems to exhaust the possible habits of 

 woody stems. Amidst all this great variety of form there is a 

 uiiiform xerophytic structure, indicating adaptation to rela- 

 tively hard conditions of living. The habitats of Gymnosperms 

 to-day indicate that they either are not at home in the more 

 genial conditions affected by Angiosperms, or have not been 

 able to maintain themselves in competition with this great 

 group. In any event, it seems clear that the conditions for plant 



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