helically

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.

在正上，枝以螺旋形绕芽生长，在子一侧接合在一形成轴，同时在子另一侧形成枝脊。