叶的主肋

The rib s of a leaf,an umbrella,a fan,a boat

叶主脉、伞骨、扇骨、船的肋材。

The ribs of a leaf,an umbrella,a fan ,a boat

叶主脉、伞骨、扇骨、船的肋材。

The differentiation states of costae indicates the ways they absorb and transport water, and their ability adapting to the dry conditions, which was elucidated by the following examples: Brachythecium plumosum, because of its thin cell-walls in the costae and the absence of hydrome, assistant and steroid cells, can absorb water and nutrition under shady and moist conditions; Plagiomnium rostratum, though often grows in shady and wet condition, has hydrome and steroid cells, a feature similar to those of xeric mosses, which endows it to grow in the conditions with periodical drought stress during its life cycle; Hygrohypnum luridum is characterized by its slender leaves with only one layer of cells, the thin cell-walls, the absence of filaments on the leaf surface, and the fewer layer cells in the costae, the absence of hydrome and steroid cells. These features make it adaptable to aquatic environments. For Pogonatum inflexum and Atrichum undulatum, their ventral surfaces covered with lamella, while for Racomitrium japonicum, Thuidium cymbifolium, Macromitrium ferriei, Diphyscium fulvifolium, Barbula unguiculata and Ceratodon purpureus, their leaves are strongly mammillose or papillos. Such appendiculate structures made them adaptable to thy conditions.

例如，荫湿生环境下的羽枝青藓Brachythecium plumosum，其中肋细胞胞壁较薄，无导水主细胞和副细胞的分化，也没有厚壁细胞分化，能够在阴湿环境下吸收水分和养分；钝叶匍灯藓Plagiomnium rostratum具有与旱生藓类植物相似的中肋结构，叶片较厚，中肋具导水主细胞，中肋背面具厚壁细胞，这些特点使该种藓类植物能够分布于间隙性干旱胁迫的环境中；水灰藓Hygrohypnum luridum叶片纤细柔弱，仅1层细胞，细胞胞壁薄，叶表无附属结构，中肋细胞层数少，无导水主细胞分化，也没有厚壁细胞，这些特点使得水灰藓'能够生长在水生环境中；东亚小金发藓Pogonatum inflerum和波叶仙鹤藓Atrichum undulatum的叶腹面覆盖着栉片，东亚砂藓Racomitrium japonicum、大羽藓Thuidium cymbifolium、福氏蓑藓Macromitrium ferriei、东亚短颈藓Diphyscium fuhifolium、扭口藓Barbula unguiculata和角齿藓Ceratodon purpureus的叶片表面有乳头状突起或疣状物，这些附属结构使它们能够适应于旱生的环境中。

The leaf structures of 17 mosses collected from different environmental conditions were transected and compared by means of paraffin wax section. The results showed that species vary much among the features such as the absence or presence of hydrome cells, the differentiation of steroid cells, the numbers of cell layer, the density of the costae, the numbers of laminal cell layer, etc.

使用石蜡切片法，对不同生境下的17种藓类植物的叶片进行了解剖观察和比较分析，结果表明不同种类的藓类植物在中肋导水主细胞的有无、厚壁细胞是否分化、中肋细胞层数及细胞密度、叶片细胞层数、叶表附属物、叶片细胞密度等方面存在显著差异。

According to the clear water experiment, aeration performance of the new equipment is good with high total oxygen transfer coefficient and oxygen utilization ratio.

曝气设备的动力效率在叶轮转速为120rpm～150rpm时取得最大值，此时氧利用率和充氧能力也具有较高值。

The environmental stability of that world - including its crushing pressures and icy darkness - means that some of its most famous inhabitants have survived for eons as evolutionary throwbacks, their bodies undergoing little change.

稳定的海底环境─包括能把人压扁的压力和冰冷的黑暗─意谓海底某些最知名的栖居生物已以演化返祖的样态活了万世，形体几无变化。