This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
When the leaves fall in autumn, transpiration ceases. Root pressure continues till all the tissues get filled with water and turgid, including the cavities of the wood fibres and vessels, which also contain air. The gradual falling of the temperature also makes the roots less active, though not entirely dormant. A considerable number of plants bloom in winter and require a modicum of water. Evergreen trees, shrubs and herbs, which retain their leaves, must have a certain supply of liquid to keep them turgid and alive. The roots themselves keep extending for an unknown length of time after the fall of the leaf, except when the ground is frozen; and what is used up in these various ways must be made good by the absorbent hairs and superficial cells of the younger roots. It is natural and necessary that the roots of plants belonging to temperate climates should have an adequate supply of water even in winter. This explains bud-dropping in Peaches that have been allowed to get over dry at the roots in winter till the buds perish, as the extremities of the trees are the first to suffer. Then when growth recommences in spring the dead buds are thrown off, if not before. Camellias suffer in the same way, in conjunction with fluctuations of temperature. If a period of dry weather succeeds the transplanting of Hollies, Laurel-cherries, Conifers, and other evergreen subjects in winter they often get killed, thus proving that the leaves give off more water from their surfaces than the mutilated roots can supply.