This computer-generated animation begins by zooming in willow tree to see a microscopic view of wood cells in one of the branches. The outer, brownish ring forms what is known as the cambium, with tension wood forming about halfway between the cambium and the centre. The animation then illustrates how tree cells form on Earth. Once on board the International Space Station, both looped and unlooped willow tree saplings will grow in space to determine the role gravity plays in the formation of different types of wood. Credit: Canadian Space Agency