Definition of PLACOID. : of, relating to, or being a scale of dermal origin with an enamel-tipped spine characteristic of the elasmobranchs. ADVERTISEMENT.Greek plak-, plax flat surface.First Known Use: 1842.efinition of PLACOID. : of, relating to, or being a scale of dermal origin with an enamel-tipped spine characteristic of the elasmobranchs. ADVERTISEMENT. Greek plak-, plax flat surface. First Known Use: 1842.
A tree pruner is a class 1 lever. The fulcrum is where the two blades cross, and the load is what you are cutting. The effort is applied to the two handles.
This is not intended to be the last word on the topic of pruning. Pruning is a four part process; how to cut, which to cut, when to cut, and how much to cut. Wind, lightning, and fire commonly injure trees. To these can be added other natural agents such as birds, insects, and animals. And finally, there are people.