. Wood; a manual of the natural history and industrial applications of the timbers of commerce. Wood; Timber. 56 OP WOOD IN GENERAL of the Forest of Dean {Q. Mobur, var. sessiliflora), are peculiarly subject to this defect, which in the latter case has been doubtfully ascribed either to the rocky character of the soil or to the swaying to and fro of the tall trees by strong winds. This action of wind bending the rings of wood alternately in opposite directions, in a manner obviously calculated to tear them apart, may well explain the occurrence of this form of shake in Poplars. Cup-shake has a
. Wood; a manual of the natural history and industrial applications of the timbers of commerce. Wood; Timber. 56 OP WOOD IN GENERAL of the Forest of Dean {Q. Mobur, var. sessiliflora), are peculiarly subject to this defect, which in the latter case has been doubtfully ascribed either to the rocky character of the soil or to the swaying to and fro of the tall trees by strong winds. This action of wind bending the rings of wood alternately in opposite directions, in a manner obviously calculated to tear them apart, may well explain the occurrence of this form of shake in Poplars. Cup-shake has also been attributed to frost, the rings of sapwood and heartwood in a living tree containing varying proportions of water and the outer layers being most hkely to freeze first. The explosive rending of trees by frost, the noise of which disturbs the stillness of night in the forests of North America, may in this way be sometimes concentric in its action. This may explain the prevalence of this defect in the swamp-loving Pitch Pine {Pinus austrdlis) of Vir-. FiG. 37.—Cup- and heart-shake, ginia. Frost cannot, however, be the cause of the frequency of cup- shake in the tropical Lignum-vitae; but in this case the sun may have produced an effect similar to that which sometimes occurs when part of the cambium ring at the base of a stem is injured by a forest fire. Lastly, in some Pines this defect is the result of the attacks of certain fungi (Trametes), the " spawn " or " mycelium " of which spreads as a felted mass of colourless mould especially in the cam- bium. Cup-shake occurs most frequently at the base of the stem : when of long standing, it is often accompanied by traces of rot, and in many cases it is also associated with star-shake. Star-shake.—Star-shaJce consists in clefts radiating from the pith along the planes of the pith-rays and widening outwards (Pig. 38). It occurs in many species and in trees of all ages. The clefts may only extend a small
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