螺旋形的

In a pennaceous feather, the barbs grow helically around the tubular feather germ and fuse on one side to form the rachis.Simultaneously, new barb ridges form on the other side of the tube.

在，枝以螺旋形绕著管状的芽生长，在管子的一侧接合在一起形成轴，时在管子的另一侧形成新的枝脊。