GENERAL PRACTICE .CLIMATE. 



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that <jf the atmosphere. From this cause the vapour of the surrounding air is con- 

 densed and deposited on their surfaces in the form of dew. This may be seen under 

 glass as well as outdoors, the blossoms of strawberries and peaches very often having 

 their petals moisture-laden when other surfaces in the structure are quite dry. The 

 deposition of dew is prevented by wind ; hence the practice of admitting a little air to 

 forcing houses, and keeping a gentle warmth in the pipes when trees or vines are in 

 flower for securing a good set of fruit. Low flat surfaces receive more dew than 

 sloping ones do ; hence blossom is killed in the hollows where it escapes injury from 

 frost on inclining higher ground. Inequalities in the surface exposure of trees, as pro- 

 vided in their differing heights, diminish radiation, and by reason of that a mixed 

 plantation of fruit trees, in standards and .dwarfs, is safer from frost than a com- 

 paratively horizontal surface of bush trees exposed to a wide expanse of sky. 



Frost. Dew frozen is hoar frost. It may freeze whilst it is depositing, after it is 

 loosely scattered on the ground, or it may not freeze for hours after it has been deposited. 

 Everything in that respect depends upon the radiation. Dew is a separation of water 

 from the air, and consequently very drying ; hence frozen blossoms can often be saved by 

 covering them so as to prevent too rapid evaporation from their surfaces in thawing. In 

 spring and autumn the greatest injury is done to fruit trees by frost. The days are suffi- 

 ciently clear and warm to cause considerable evaporation, and the nights are corres- 

 pondingly clear ; therefore, there is the radiation from the earth, blossoms, foliage, or 

 fruit, as the case may be, and it follows that as heat passes out cold comes in. 



The effect of frost on blossoms and tender foliage is to give them a blighted appear- 

 ance as if scorched by excessive heat. Their tissues are ruptured through the water 

 they contain freezing, and their vesicles are destroyed. Sometimes only the superficial 

 layers are damaged, and then the leafage assumes a whitened appearance, the outer 

 covering or cuticle having parted from the inner layers of the epidermis. Such is seen in 

 the " silver leaf " of plums. Frost, therefore, is injurious in proportion to the water in the 

 plant tissue. It is most disastrous immediately after rain, and to trees growing in rich 

 moist soils and damp situations where their foliage and blossoms are full of sap. Late 

 growths, being soft, are damaged, and show scars sooner or later, but the resistance of 

 firm wood to frost is exceedingly great. Frost is very injurious to fruit as food. The 

 more tender and juicy it is, the greater the liability to depreciation. Some kinds of 

 fruit, however, are best left to mature properly on the trees. Such apples as Dutch 

 Mignonne, Cox's Orange Pippin, Nonpareils, Pearmains, and Kussets do not suffer from 



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