RESTING VEGETATION. 



399 



persons, and the glass being much less liable to be broken, and requiring no 

 covering during nights, it is found to be on the whole more economical than 

 common glass, and much better for the plants. 



853. The annual resting of plants is effected, as we have seen, either by cold 

 or by dryness, and both these causes can be imitated in a state of culture, 

 either separately or combined. Plants in the open garden may be safely left 

 to the influence of the seasons ; but half-hardy plants against walls, or in 

 borders by themselves, may be brought to a state of rest by thatching the 

 ground so as to prevent what rain may fall on it from sinking in ; the lateral 

 supplies being cut off by surface gutters or underground drains. The supply 

 of sap by the roots being thus reduced, growth will gradually cease, and the 

 parts will be matured, and at once enabled to resist the winter and vegetate 

 with redoubled vigour the following spring. It may be observed here that 

 the shoots of a tree which is to be protected from frost during winter, do not 

 require to be ripened to the same degree with shoots which are to be exposed 

 to the action of frost in the free atmosphere ; because buds, like seeds, will 

 vegetate provided the embryo be formed, even though they should not be 

 matured. Plants which have been forced have their period of rest brought 

 on naturally by the maturation of the plant, and artificially by removing the 

 glass with which they are covered, and exposing them to the free action of 

 the atmosphere, which at that season being dry, is much more favourable for 

 evaporating the watery part of the sap than it is later in the autumn ; and 

 hence peach-trees which have been forced, have almost always better-ripened 

 wood, containing more blossom-buds, than peach-trees on the open walls. 

 In the case of peach-houses, vineries, &c., the glass roof is removed and the 

 plants left in their places ; but where vines are grown in a hothouse or 

 greenhouse along with other plants that require artificial heat throughout 

 the year, the shoots are withdrawn and exposed to the common atmospheric 

 temperature for three or four months. Greenhouse plants, such as natives 

 of the Cape of Good Hope and Australia, are brought to a state of rest, 

 partly by lowering the temperature of the greenhouse and partly by with- 

 holding water. The last mode is that which is most to be depended on, 

 because in most greenhouses there are some plants in flower at every period of 

 the year, and for these a greater degree of heat must be kept up than would 

 suffice alone, for throwing greenhouse plants into a state of rest. All tropical 

 plants are brought to a state of repose by dryness, and this is readily imitated 

 in hothouses, in consequence of the plants being in pots. There are some 

 tropical plants, however, which though in certain localities they have what 

 almost amounts to a short cessation of growth, yet in a state of culture they 

 succeed better without it. Of these plants the pine-apple is one which 

 when kept in a state of active growth till it has produced its fruit, brings 

 it to a far larger size than when allowed a period of repose ; and this would 

 appear to be practicable with all ligneous plants that are without buds ; such 

 as most endogens, in which class of plants buds are chiefly found among 

 herbaceous species in the form of bulbs. 



854. The natural period of rest in hardy plants may be varied or changed 

 by withholding moisture, even without reference to temperature. We see 

 this taking place both with trees and herbs in dry seasons : when wood is 

 ripened, leaves drop off; and grass fields become brown, in July and August, 

 which in moist seasons would have continued growing till October or Novem- 

 ber. By imitating these effects in gardens, the operations of accelerating 



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