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教学要点就是本课教学的主要观点和基本内容教学重点是指几个教学要点中，占主要地位的那个要点。在几个教学要点中，学生很难理解或难以做到的那个要点，就是教学难点。 相似文献
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在扫描电镜下,比较观察了冷杉属全世界36种2变种的叶角质层内表面的结构特征,根据叶角
质层内表面胞间凸缘特征的显著差异,将冷杉属植物归为4类:(1)直且发达的单凸缘;(2)双凸缘;
(3)不发达的单凸缘;(4)弯曲且发达的单凸缘。并发现这四种凸缘类型在冷杉属中的分布格局与该
类植物的地理分布具有相关性。根据所观察的结果和前人的属下分类系统以及化石资料,认为北美西部是现代冷杉属植物的一个多样性中心。 相似文献
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傅立国 《中国科学院研究生院学报》1984,22(4):277-288
The genus Cephalotaxus contains a small number of species. It is adequately
appreciated as a newly discovered cancerresistant medicament for the alkaloids obtai-
ned from its branches leaves and barks are of curative effect.
This paper deals with the classificatory revision based on the morphological featu-
res, with the reference to the anatomical characters of leaves, types of alkaloids and
pollen morphology observed. Two new combinations are proposed, and 4 species and
varieties are reduced in the paper. The genus Cephalotaxus is thus suggested to consist
of 2 sections and 9 species. The trees occur in East Asia and the north of Indo-China,
with 88% found in China where is the distribution centre and refuge of the genus.
The genus in discussion is of unique morphological features which are distinctly dif-
ferent from these of Amentotaxus, Cephalotaxaceae, containing a single genus of Ce-
phalotaxus, is closely related to Taxaceae, and therefore the Cephalotaxaceae is best
placed in the Taxinieae of Coniferales. 相似文献
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