6o THE FRUIT GROWER'S GUIDE. 



frost to anything like the same extent as do the soft-fleshed sorts, fruits being acted on 

 much in the same way as wood, but frost generally deprives fruit of its pleasant taste and 

 it soon decays after being thawed. This applies equally to fruit preserved in ice or kept 

 in ice-houses ; it loses taste, quality, and decays quickly on thawing. Saline juices render 

 the tissues of fruit less liable to congelation by frost ; consequently apples containing 

 26-09 per cent, of soda resist frost better than pears that contain only 8*52 per cent. 

 Trees on the coast for similar reasons are less susceptible to damage by cold than are 

 those at a distance from the sea. 



Light. Fruits are excellent in proportion to the solar light received. In a dull season 

 they may be large yet not bright, but in a sunny year, colour, sweetness, and high 

 quality are most pronounced. Light acts chemically upon fruit trees ; leaves excluded 

 from light become unhealthy, and hence they seek it, always turning their upper surfaces 

 to where there is most, and shoots from the interior of a tree always make direct for 

 the opening through which they receive light. In the ripening process light is a neces- 

 sary factor, and it is of such importance that it is essential to promote its efficacy as 

 much as possible by the removal of useless growths and overshadowing leaves, also by 

 the use of clear glass, and surfaces that reflect the light upon whatever may be grown 

 in glazed structures. 



Heat. Heat is a primary agent in the production and perfecting of fruit. Air expands 

 with the increase of temperature, or for a rise of 4 it expands twice as much as for a rise 

 of 2 9 , and this is the main source of energy in vegetation. It is, however, with heat 

 radiation that fruit growers are or should be most acquainted. It is transmitted 

 by the same medium that light is, and obeys the same laws of reflection, refraction, 

 interference, and polarisation. Falling on a translucent substance, such as glass, rays 

 pass through without heating it ; but falling on an opaque substance, such as a wall, they 

 are absorbed and the substance becomes warmed. Some bodies lose heat more rapidly 

 than others, but as a rule good absorbing surfaces are good radiating surfaces. Glass 

 admitting light and heat to pass through freely lets the heat out quickly, but if we 

 interpose a non-conducting material we shut out the heat by day, as is done in shading, 

 and preserve it at night, as is done in protecting. A woollen net is a better protector 

 than hemp, making a difference of 2 or 3 under an identity of circumstances. But 

 despite everything contrived for rendering more effectual the natural temperature offered 

 by our climate, artificial means of securing sufficient heat for the successful forcing of 

 hardy, as well as the cultivation of the semi-tropical or tropical fruits, are imperative. 



