REFERENCE TO HORTICULTURE. 45 



on surfaces sloping to the south ; and on surfaces elevated and freely 

 exposed, rather than in low and confined situations, in which light is 

 obscured by surrounding objects or by aqueous vapour. The light 

 thrown on the leaves of a plant in the open air may be increased by 

 surrounding it on the north, and part of the east and west sides, by a 

 wall or other upright surface painted white, or covered with glazed 

 tiles or tinned iron. Practically, however, the grand means of increas- 

 ing the efficiency on plants of such light as there may be in any given 

 situation, is by training them against walls, espaliers, or on the surface 

 of the ground ; or, for those that cannot be conveniently so trained, 

 by removing all other plants and objects which are so near them as 

 either to obstruct the sun's rays or to interfere with reflection. To insure 

 the full effect of the reflection of transfused light upon a plant, it ought 

 to have a free space around it, in width on every side at least equal to 

 its own height. No timber tree which has not at least this space can 

 receive from light the full influence which it ought to have on its hori- 

 zontal branches; and hence the trees in dense forests must necessarily 

 produce timber inferior in bulk to those of the same kinds, in the same 

 climate and soil, which are grown as single trees in parks, or in hedge- 

 rows. 



In plant-structures a due proportion between light and heat ought, 

 as much as possible, to be preserved, because this is always the case in 

 nature, where both depend on the sun. It is not in our power to 

 increase the natural light of the atmosphere, for the great disadvantage 

 to which horticulture is subject in this climate is the uncertainty of 

 clear weather ; but artificial warmth can be supplied or withheld at 

 pleasure. 



The absence of light, as we have before mentioned, is necessary to 

 render certain bitter or unwholesome parts of plants fit for culinary 

 purposes ; and the diminution of light is frequently had recourse to, 

 when the habitation of plants which grow in shady places is to be 

 imitated, and when the perspiration from the leaves of plants is to be 

 diminished. In all cases of rooting plants from cuttings which have 

 the leaves on, the diminution of perspiration, by shading them from 

 the direct rays of the sun, is necessary, till the cuttings have taken 

 root ; and this is also more or less the case with all rooted plants 

 which are removed with the leaves on, for some days after transplant- 

 ing. \Vhen plants are in a dormant state, and without leaves, no 

 light is requisite to maintain them in a healthy state ; and even such 

 evergreens as are in a state of comparative rest require very little. 

 Hence orange-trees and other greenhouse evergreens, may be kept 

 through the winter in an opaque-roof conservatory ; and deciduous 

 plants, which have lost their leaves, may be kept through winter in 

 nouses or in cellars into which no light is admitted. In the absence 

 of light, however, a low temperature must be maintained: with the 

 clear glass and light roofs of the present day, more shading is needed. 

 There are many plants cultivated that cannot bear the fierce glare of 

 the sun, and a subdued light is essential to the prolongation of the 

 blooming period of most plants. 



