ONE OF the excitements of a visit to the West Country and Cumbria is seeing ferns growing naturally in the forks and along the branches of trees. In areas of high rainfall the native polypody (Polypodium vulgare) will do it easily. But even in drier areas the effect can be contrived. Set 2-3 square inches of fern in a shady fork now, on a pancake of dung, soil and moss, and tie it on with soft string. The fern will not have made any new growth yet and will put out new fronds in due course. Given a wet year or an occasional artificial soaking it will grow hard next year.