In both types of feather, the barbules that extend from the barb ramus grow from a single layer of cells, called the barbule plate, on the periphery of the barb ridge.
FiloBot mimics these behaviours using sensors in its head—at the tip of the main shoot—which is also equipped with a spool of plastic and a heating element.
How well they sing in the wind, and how strikingly harmonious an effect is made by the immense cylindrical cones that depend loosely from the ends of the main branches!
The largest of the main branches is eighteen feet and nine inches in circumference, and some of the long pendulous branchlets droop over the stream at the foot of the fall where it is gray with spray.
左右两边各向不
向生长。
山（上） 
何种羽毛，从羽
们在
唱得多么美妙，从
