Just outside the fence on the south-west corner of our garden there's a large Norway maple whose winged seeds are scattered all over our vegetable patch by south-westerley gales in autumn. All winter hundreds of seeds have been laying on the soil surface, buried by snow and dusted with frost crystals, and recently they've all begun to germinate, pushing out their first root into the soil. If we didn't cultivate this patch of ground every spring we'd have a small forest of Norway maple by now; some, behind the greenhouse, have escaped the hoe in earlier years and are on the way to becoming small trees.
Like many plants, the dormant seeds of Norway maple are incapable of germination when they're shed and it takes a winter's frosts to break down the dormancy compound - abscisic acid - inside the seed and allow germination to begin, just as the temperatures begin to rise in spring.
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