Answer: Witches Broom is a proliferation of growth, generally due to an injury and the invasion of fungi. I wouldn't use an affected branch as stock for a new tree! According to James Dirr's Manual of Woody Plants, 6 to 8 inch softwood stem cuttings should be taken in July, wounded, treated with a strong rooting hormone, and stuck into a peat and perlite potting mix. They should be kept under mist until they have rooted (this can take months) at which point they should be left alone to undergo a normal winter dormancy or should be set under supplemental light and encouraged into active growth.
It is possible to take root cuttings, but these are very difficult to root, which is one of the reasons the majority of maples are grafted rather than on their own roots.
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