THE RELATION OF CLIMATE TO POMOLOGY 239 



Several factors determine at what temperature such in- 

 jury occurs, for it is well known that it is not consistent. 

 The amount of moisture in the atmosphere at the time of 

 frost is conmionly cited as of the greatest importance, the 

 greater tlic humidity the less likely will there be injuiy. Also 

 the individuality of the plant may enter into the problem. 



West and Edlefsen conmient as follows in regard to this 

 phenomenon: "The fact that the same branch of buds will 

 on one occasion experience 27° F. with 25 per cent injuiy 

 and on another occasion take the same temperature with 

 no injuiy is no doubt due to the fact that the juice is con- 

 tained in capillaiy cells and supercooling results — that is, 

 the buds are cooled below the freezing point of the juice 

 without the freezing taking place. The great difficulty of 

 killing all the buds even at extremely low temperatures is 

 due to the same cause together with the fact that the cell 

 sap may be very concentrated. Differences in the hardi- 

 ness of the different kinds of buds and also of the same buds 

 at different stages of development is due to differences in 

 quality and concentration of the cell sap." 



It is easy to overestimate the damage at the time of the 

 low temperatures, for no means are available for determin- 

 ing the extent of injuiy unless the floral parts (usually the 

 pistils first) are blackened or withered. Orchards in which 

 the blossoms seemed entirely destroyed may still set a fair 

 crop of fruit. 



209. Averting injury from frosts and freezes.^ — Attempts 

 are sometimes made to avert injuiy to the fruit crop from 

 spring frosts by various devices. Whitten ^ whitewashed 

 peach trees to delay their blossoming, with some success. 

 The principle made use of here is that a white surface will 



' See papers on frosts and frost protection in U. S. U. S. Dept. Agr. 

 The Monthly Weather Review, 42: 562-592. 1914. 

 2 Mo. Agr. Exp. Sta. Bull. 38. 1897. 



