Balsam fir is a common Christmas tree species, since the needles are fairly soft to the touch compared with spruce. The needles are about 2 cm long, flat, and have faint white lines on the underside. Each needle is individually attached to the twig, and will leave a circular scar when they fall off. Cones are held upright. Fir trees have smoth, brown bark that has many raised bumps which contain resin to protect the trees from insects, which get stuck if they chew at it. This is the same substance that becomes amber. Hemlock has similar, but much shorter, needles and spruces have sharp needles which are four-sided in cross-section, not flat.