细话裸子植物OACSTPCD

In the botany textbooks,generally only a few pages are used to describe Gymnospermae,but there are many problems in this chapter troubling teachers and the students.This paper reveals contradictory statements regarding taxonomy of Gymnospermae in the textbooks and provides some suggestions for revi-sion.Firstly,the stems of gymnosperm plants should possess a eustele rather than a dictyostele.Secondly,evolutionary origins of several kinds of leaf types in gymnosperms are speculated based on their develop-mental heterophylly.Then the reproductive structures and development of cycads are carefully analyzed,and some confusion is clarified.Furthermore,the pine life history is discussed in detail,and some inaccurate statements are corrected.The significant issue of whether ovules develop from modified leaves or stems is also discussed.Finally,the phenomenon,which appears in the genera Ephedra and Gnetumin,that two sperms in a pollen tube participate in fertilization should be called"double fusion"rather than"double fer-tilization.