PROTECTION AGAINST FROST 363 



Emery ,^2 in Montana, found injury in strawberry varieties ranging from 12 

 per cent, to zero. Tlie date of bloom in this case seems to have had little effect, 

 since Warfield, one of the earhest blossoming of the 58 varieties under observa- 

 tion, escaped all injury. Wilcox^i^ at the same station found the anthers of 

 certain varieties injured by frost; the tissue in which the pollen grains were 

 embedded ruptured and a small proportion of the pollen grains were killed. Some 

 injury was observed in styles and stigmas, probably enough to interfere with 

 their functioning. In blossoms which had been fertilized the injury was confined 

 to the akenes; in no case was the receptacle injured. The akenes became dis- 

 colored rapidly. In resistant varieties they were so deeply imbedded in their 

 pits as to be practically surrounded by the pulp. Tender varieties had their 

 akenes most exposed or in very shallow depressions. Between these extremes 

 there was a regular gradation. It thus seems possible that a variety may be 

 resistant at one stage — before fertihzation, for example — and yet be tender at 

 another stage, say, after fertilization. 



Vigor and Recuperative Ability. — The vigor of the tree is stated 

 frequently to be a factor in the damage produced by frost. This opinion 

 may be founded on observations of the crop the weak trees bear and in 

 failure to recognize that, frost or no frost, such trees fail often to set a 

 large percentage of fruit. A series of freezings of blossoms from strong 

 and from weak Gano apple trees indicated no superior hardiness in blos- 

 soms from the more vigorous; in fact the average of the various tests 

 was very slightly in favor of the weak trees.^^ In herbaceous plants, 

 injury sometimes appears more pronounced in those making a less 

 vigorous growth, but in all probability the observed difference is due 

 to the superior recuperative powers of the more vigorous plants. There 

 is some indication that plants treated with nitrate of soda recover from 

 frost damage better than others. This recovery is, however, in the vege- 

 tative portions. There is, occasionally, a fairly large second bloom on 

 apple and pear trees following a frost, but this is the exception and ap- 

 parently it is not related to vegetative vigor. Recuperative power is of 

 little immediate benefit to the grower once the blossoms are killed. 



Weather Conditions Before and After Freezing. — The weather pre- 

 ceding and immediately following the freeze may be factors of some 

 little impoi'tance. 



Pf offer'", speaking of plant tissues in general, says: "The resistance to 

 cold depends to a certain extent upon the present and previous external 

 conditions. Thus Haberlandt found that seedUngs grown at 18° to 20°C. 

 froze more readily than those grown at 8°C." Rosa^'^^ found that cabbage 

 grown in a greenhouse at 20°C. killed when exposed to -4°C. for 1 hour 

 while plants grown in a cold frame were uninjured by exposure to _the same 

 temperature for over 2 hours. It seems reasonable to suppose that the 

 same principle applies to fruit blossoms. Garcia''^ records that a temperature 

 of 24.75°F. at 2 a.m. followed by a rise to 31° at 5:30 caused less than 3 per 

 cent, injury to Alexander peach blossoms which were in full bloom at the time, 



