In cross-sectioned root form 2 middlebark layer next Internal bark layer especial structure of regularly array;
根横切面上形成了在紧靠内皮层的两层中皮层细胞有规则整齐排列成两环的特殊结构；
2
Then, with the tip of the knife, he carefully carved a tiny hole in the middle of the bark.
接着，他小心翼翼地用小刀的尖端在树皮的中间穿了一个小孔。
3
And then they scampered in all directions, for Toto had awakened from his sleep, and seeing all these mice around him he gave one bark of delight and jumped right into the middle of the group.