GENERAL PRACTICE. TEMPERATURE AND VENTILATION. 61 



Temperature. The temperature and rainfall of these islands are now so well defined 

 that we do not think any good purpose would be served by entering into them, but 

 there is the question of artificial temperature that cannot be passed. The ascent of the 

 sap and its circulation is increased or decreased by the temperature to which fruit trees 

 are subjected. In nature trees are active by day and repose at night. If the night is 

 cold comparatively to the day the sap sinks back. Heat, therefore, acts as a stimulant 

 and cold as a sedative. No greater proof of the need of rest is afforded than the fact 

 that wherever a tree grows naturally it is subjected to daily alternations of temperature. 

 The day temperature is usually 10 to 20 higher than the night during the period of 

 active growth and maturity of crop. Usually the greater the day temperature the lower, 

 proportionately, is that of the night. During dull days or in genial weather, when the 

 air is moist and warm, vegetation is rapid. Knowing that, the cultivator of fruit under 

 glass closes his houses early to incite growth and assist the fruit in swelling, taking care to 

 afford no more heat at night than suffices to sustain the health and progress made, so that 

 the peach or vine may be strengthened and refreshed, and with the heat of day derive sub- 

 stance either in the form of solidified wood or concentrated juices in the fruit. Sudden 

 fluctuations of temperature should be studiously avoided, especially in conducting forcing 

 operations, and unremitting attention is needed when the weather is fitful and alterna- 

 tions of heat and cold are sudden and extreme, or the hopes of the cultivator cannot be 

 realised. 



Ventilation. Although growth may luxuriate in confined structures, trees and vines to 

 be healthy and fruitful must have air. This is essential to prevent a weak condition 

 of the tissues and to give firmness to the growths. Upon this depends very much the 

 health of the trees, their flowering satisfactorily, the fecundation of the blossoms, and 

 the quality and flavour of their fruit. Air should never be admitted in such a volume 

 as to lower the temperature, but only to prevent it becoming too high. Ventilation 

 should commence early, or as soon as the sun makes its influence felt on the house. 

 This is absolutely essential to the production and preservation of sound foliage, and 

 neglect or mismanagement results in scorched leaves and other misfortunes. Air 

 should be afforded, as far as possible, so as not to produce a cold driving current 

 against tender young growths, and it is always better to allow a few degrees of sun 

 heat above the ordinary range than to admit cold air in quantity by the ventilators to 

 reduce the temperature to a given figure. It is most unwise to admit air at 75, so 

 as to bring the temperature down, to a house which ought to have been ventilated 



