PROCEEDINGS OF TWENTY-STXTH FRUIT-GROWERS' CONVENTION. 113 



while thermometers six feet above the ground will record 34° or 35° F. 

 Vegetables and flowers, therefore, unless grown upon sloping or terraced 

 ground, are at a decided disadvantage compared with tree fruit in the 

 matter of frosts. 



Nature of Frost. — It can not be emphasized too clearly that it is 

 the low temperature and not the solidification of the water which does 

 the damage. If there be but little vapor in the air there will be but a 

 light frost apparent, and yet the temperature may be so low as to cause 

 great injury. The so-called hard, dry frost, also called black frost, does, 

 as is well known, even more injury than heavy frosts. Water vapor at 

 25° completely saturated weighs 1.6 grains per cubic foot. In the fall 

 from 32° to 25° nearly half a grain per cubic foot, if the saturation were 

 100 per cent, would be condensed, appearing in visible form as frost 

 flakes. A certain amount of heat was given off in the transformation of 

 this visible water vapor into ice, and an exactly equal amount of heat 

 (known as the latent heat of vaporization) will be in turn required to 

 change this frost flake back into vapor. We give special attention to 

 this point, because it would appear theoretically that the secret of suc- 

 cessful protection of garden truck and delicate flowers will be found in 

 this action of water, both in setting free heat at the time when the tem- 

 perature is falling, and on the other hand in using up heat and thus 

 acting as a retard or brake when the temperature begins to rise quickly. 



It is now quite generally believed that as much injury results from 

 the sudden warming up of the dormant and thoroughly chilled flower, 

 fruit, or vegetable as from the chilling itself. In the work of protect- 

 ing fruits from frost it has been found very necessary to interpose 

 some screen early in the morning between the sun's rays and the frosted 

 fruit. With flowers and garden truck this can be much more easily 

 accomplished than with fruit. In this respect the gardener has a 

 decided advantage over the orchardist. The following is an excellent 

 statement of how the plant is injured: 



How Frost Injures Plants. — "Low temperature congeals the watery 

 part of the cell sap and also the intercellular water content of the plant. 

 Within certain limits this is not or may not be injurious, providing 

 the protoplastic contents of the cell are able to absorb the water and do 

 this before the cell structure collapses as a result of insufficient cell 

 turgor. Frequently the frosting of plants is followed by a sudden rise 

 in temperature, in which case much of the water which was part of the 

 cell sap in the normal condition of the plant escapes through the cell 

 wall into intercellular spaces, or even from the plant entirely, and thus 

 the protoplasm of the cell, being unable to assume its normal condition, 

 becomes disorganized, and decomposition follows."* 



♦Professor E. R. Lake, in the Oregon Climate and Crop Bulletin, July, 1900. 

 8 — F-GC 



