Lines for all of the grey pencils were drawn vertically, following the length of the trunks. To blend all of the layers together, I used a horizontal stroke following the curve of the trunk.
I blended the Aspen trunk's characteristic black bumps in with their shadows, which had been constructed using the various shades of grey. When blending black with another color, you have to be very careful because the end of the Colorless pencil can pick up traces of the black and then smear it across the lighter colored areas. After blending with a black area, I rub my colorless pencil on a blank paper to remove all of the black color, before proceeding with the blending of the lighter colors.
The picture is FINALLY complete. If you've followed along and have completed your drawing, too, CONGRATULATIONS!
If you haven't, then Get Crackin'!