The roots of many orchids and other epiphytes developed a sheath of dead cells , the velamen , which helps to absorb water from the atmosphere 许多兰科植物的根和一些附生植物的死细胞鞘以及根被都可以帮助植物从空气中吸收水分。
2.
Root of backbone nerve around is in backbone ganglion is far side assemble , scabbard of stiff backbone film also closes subsequently for one scabbard , become backbone nerval velamen , namely the film outside nerve , because backbone ganglion is located in between vertebra kong shuiping , the length of backbone nerve root has variation consequently 脊神经前后根在脊神经节远侧会合，硬脊膜鞘也随之合为一鞘，成为脊神经的被膜，即神经外膜，由于脊神经节位于椎间孔水平，脊神经根的长度因而有变异。
