416 THE PAEKS AND GAEDENS OF PAEIS. [Chap. XXIV. 



with walls ; . but no such thing. They find them indispensable for 

 the perfect culture of the finer Winter Pears ; and were they not 

 to use them, they could never obtain such a stock of these as they 

 have. Yet we have for a long time past been paying attention to 

 almost every kind of garden-improvement except this important 

 one. It is true that walls are expensive, but once reared it is a 

 great pity to neglect them ; and, apart even from garden- walls, 

 there are numerous places with as much wall-surface naked and 

 useless as, properly covered, would yield a good supply of fruit. 

 Few things combine beauty and utility more than a well-covered 

 wall of Pear-trees ; and the creation of such is not a matter of 

 difficulty. With walls it may safely be said that our climate is as 

 good as that of Northern France. Most large gardens would be 

 benefited by having a much greater proportion of wall-surface 

 than they have at present ; to many small ones they would also 

 prove a desirable addition. 



Of whatever material the wall be made, it will be desirable to 

 whiten its surface and keep it white. Black and dark-coloured 

 surfaces absorb heat in the daytime, and give it out again during 

 the night in the form of radiant heat ; from which facts we might 

 perhaps conclude that walls for training fruit-trees should be 

 black, or at any rate of a dark colour. Direct experiment was, 

 however, necessary to settle this question, and M. Vuitry, who 

 employs his leisure in arboriculture, communicated the results of his 

 experiments in this direction to M. du Breuil, leaving no doubt as 

 to the proper colour to be chosen for walls against which fruit-trees 

 are to be trained. He has proved— 1st. That a thermometer 

 hung during the day with its face turned towards a white wall, at a 

 distance from it equal to that of a fruit-tree trained against it — 

 i.e., about an inch and a quarter — always showed a mean tempera- 

 ture of nearly 6 deg. Fahr. higher than one hung against a black 

 wall under precisely similar circumstances. 2nd. That during 

 the night the difference of temperature shown by these two ther- 

 mometers was inappreciable. Contrary therefore to the opinions 

 entertained by many persons, it seems evident that the walls 

 must be whitened when we wish to give the trees trained against 

 them the maximum amount of heat to be obtained in the par- 

 ticular climate and aspect. Indeed, it is precisely the plan that has 

 already been pursued by the fruit-growers at Montreuil for Peach- 



