Less Is MoreIt sounds all wrong－drilling holes in a piece of wood to make it more resist'ant to knocks. But it works because the energy from the blow gets distributed throughout the wood rather than focusing on one weak spot. The discovery should lead to more effective and lighter packaging materials.Carpenters have known.____（51） centuries that some woods are tougher than others. Hickory （山核桃木）, for example, was turned into axe handles and cartwheel spokes （轮辐） because it can absorb shocks without breaking. White oak, for example, is much more easily damaged,____（52） it is almost as dense. Julian Vincent at Bathe University and his team were convinced the wood's internal structure could explain the differences.Many trees have tubular （管的） vessels that run____（53） the trunk and carry water to the leaves. In oak they are large, and arranged in narrow bands, but in hickory they are smaller, and more evenly distributed. The researchers.____（54） this layout might distribute a blow's energy throughout the wood, soaking up a bigger hit. To test the idea, they drilled holes 0.65 millimetres across into a block of spruce （云杉）, a wood with____（55） vessels, and found that____（56） withstood a harder knock.____（57） when there were more than about 30 holes per square centimetre did the wood's performance drop off.