He's describing the ends of an ash tree in the fall. He's saying that the pattern of it looks like a skeleton. The spray-end is the end of the branch that has leaves and seeds(keys). He broke off a piece at Wimbledon and sketched it in his journal. The shape of it reminds him of a globe. I think what he broke off is something like this: http://www.sciencephoto.com/image/33897/350wm/B7870461-Ash_tree_seed_cases_Fraxinus_excelsior_-SPL.jpg