Line direction is where flowers placed in the design giving the arrangement vertical direction, horizontal direction, or a diagonal line. Line materials also place curves into the flower design. Without line in a design, we would not have any fluid movement. Our eyes would be stuck and not circulate throughout the design to see the whole image we are trying to create.
You could create an arrangement for any size vase, the larger the vase, the more flowers and greens to use. For Christmas time, use red, white and maybe even green flowers (like green button mums). Also choose from a variety of greens and evergreens out there. Accent a red rose in a bud vase with some baby's breath and cedar. Deep red alstroemeria are especially beautiful. There are many other flowers that would be perfect to use for Christmas arrangements, the link below will take you to a complete list of flowers, foliage, and evergreens for Christmas floral design.