巨杉的叶表皮结构及其与红杉和水杉的比较

杉科植物巨杉是美国特有植物.叶片鳞状钻形，双面气孔型.叶面非气孔区的表皮细胞长方形，细胞长轴与叶片长轴的方向一致.叶片远轴面和近轴面各有2条气孔带，每条气孔带由2～5行气孔组成.叶片中部的气孔带最宽，气孔数量最多.叶片顶部近轴面的气孔数量比远轴面的气孔数量明显多，叶片中部远轴面和近轴面的气孔分布和数量近似，叶片基部远轴面的气孔明显比近轴面的气孔多.气孔椭圆形，多数气孔的长轴与叶片长轴的方向一致.保卫细胞肾形，细胞壁加厚.副卫细胞的形态特征和垂周壁的角度与周围表皮细胞的不一致.巨杉与其近邻北美红杉和中国特有植物水杉相比，巨杉和北美红杉的表皮细胞壁直，水杉的多数表皮细胞的壁明显弯曲；巨杉叶表皮细胞的大小与水杉的近似，而北美红杉表皮细胞的长度明显比巨杉和水杉表皮细胞的长度大；巨杉叶片的远轴面和近轴面都有气孔分布，水杉的气孔主要分布在叶片的远轴面；北美红杉既有类似巨杉的气孔分布方式，又有类似水杉的气孔分布方式；巨杉气孔的形态和大小与北美红杉的更近似. 

Epidermal structure of giant redwood and its comparison with those of coast redwood and dawn redwood

Giant redwood(Sequoiadendron gigantean),the only living species of the genus,is endemic to the United States.The leaves of giant redwood are scale-subulate and amphistomatic.The epidermal cells are rectangular within the non-stomatal areas,and the long axis of epidermal cells is parallel to that of leaves.Two similar stomatal bands distribute on each of the abaxial and adaxial surfaces of leaves.Most stomatal bands comprise 2-5 lines of stomata,and the widest part of stomatal band is located on the middle part of the leaf.The number of stomata on the adaxial surfaces is more than that on the abaxial surfaces in the top part of leaf,but the number of stomata on the adaxial surfaces is less than that on the abaxial surfaces in the base part of leaf.The number of stomata on the adaxial surfaces is about the same as that on the abaxial surfaces in the middle part of leaf.Stomata and pores are elliptic.The long axes of most stomata are parallel to those of leaves.Guard cells have thick walls,especially on the outer margins.The subsidiary cells are different from the epidermal cells in morphological features and the angle of insertion on the view of scanning electron microscopy(SEM),so the subsidiary cells show a very distinctive oval or round appearance on the inner surface of cuticle.Compared with the epidermal structures among giant redwood,coast redwood(Sequoia sempervirens,the neighbor species of giant redwood) and dawn redwood(Metasequoia glyptostroboides,native species of China),the anticlinal walls of epidermal cells are mostly straight in giant redwood and coast redwood,but they are obviously undulate in dawn redwood.The size of epidermal cells in giant redwood is similar to that in dawn redwood,and it is apparently smaller than that in coast redwood.Most stomata locate on the abaxial surfaces of leaves in dawn redwood,and they locate on both the abaxial and adaxial surfaces of leaves in giant redwood.As the stomatal distribution,some leaves in coast redwood are similar to those in dawn redwood or in giant redwood.The stomatal morphology and size in giant redwood are more similar to those in coast redwood than to those in dawn redwood.