OBSERVATIONS ON FROST INJURIES 501 



ficially freezing thousands of peach buds, summarized the critical tem- 

 peratures as follows : 



"Fully dormant peach buds can stand 8 or 9 below zero, F. When they 

 are appreciably swollen, zero is the danger point. When the buds are showing 

 pink, they can stand 15 above zero. When the buds are almost open, 25 is 

 the danger point. When they are newly opened, about 26 would be the point 

 of danger. When the petals are beginning to fall, 28 above zero is dangerous. 

 When the petals are off they can stand 30 above zero. When the 'shucks' 

 (calyx lobes) are beginning to fall off, 32 is the danger point." Presumably 

 these limits would apply also to the apricot and almond. 



Apple buds, when the petals begin to show, can stand from 10 to 12 degrees 

 of freezing. When the petals are well emerged, but have not opened, they can 

 stand from 4 to 6 degrees of freezing, but when open, but not yet fertilized, 

 there would be great danger at two or three degrees below the freezing point. 

 When the flowers have been fertilized, the petals dropped, and the young fruit 

 increasing in size, the slender stems which support the apples are unable to 

 resist a temperature lower than the freezing point. The apples seem to be 

 more hardy than their stems, but if the latter are injured of course the fruit 

 also suffers. Similar behavior may be expected from the pear, cherry and plum. 



Orchard Frost Studies. In connection with the foregoing it is 

 interesting to note conclusions which Prof. Fabian Garcia draws from 

 several years' observation of frost effects in the orchard of the New 

 Mexico Experiment Station and of which full details are given in 

 Bulletin 89 of that station, under date of February, 1914 : 



The data recorded at the Station show that the fruit-buds, particularly those 

 of the peach, at their different stages of development are somewhat more resist- 

 ant to cold than has been reported by observers from others parts of the United 

 States. The data further show that the degree of resistibility to frost varies 

 with different stages of growth. 



The peach is least resistant when it is about the size of a pea, when the 

 calices are falling off. Contrary to the findings of other observers, the bloom 

 is not the most tender stage of growth. In other words, the data indicate that 

 the newly set peach is more delicate than the newly opened blossom. 



In the majority of cases a temperature of 26 degrees, lasting only a short 

 time, did little or no injury to the opening bud, newly opened blossom or newly 

 set fruit of the peach, native plum, pear and apple; while one-half a degree 

 below this, or 2$*/ 2 degrees, although lasting only a few minutes, killed a large 

 percentage of the opening buds, newly set blossoms and young fruits of the 

 peach, in a number of cases. In other words, 26 degrees was the danger point, 

 and any temperature below this is liable to do more or less injury; depending 

 on how low it gets and how long it remains at that temperature. In some cases, 

 however, a temperature of 24 degrees lasting only a short time left about 25% 

 of the blooms and 9% of the newly set fruits uninjured. 



Three important factors that influence the amount of damage done by spring 

 frosts are : the degree of killing temperature, the time of day at which it occurs, 

 and the length of time the temperature remains below the danger point. The 

 longer the time the killing: temperature remains and the nearer it is to sunrise, 

 the greater the amount of damage that should be expected. 



As a rule, the killing temperature recorded in these experiments occurred 

 in the morning, from one to two hours before sunrise. Whenever the killing 

 temperature occurred this late in the morning, and remained below the danger 

 point until sunrise, the injury was great. On the other hand, if the minimum 

 occurred at midnight, or a little later, and then gradually rose to the freezing 

 point, so that the frozen buds, blooms and fruits had time to thaw out slowly 

 before sunrise, the injury was insignificant. This was the case April 5, 1910, 

 when at 2:15 A. M. the temperature was 24^4 degrees. By 5:30 it had risen to 

 31 degrees, and the injurv done to the Alexander peaches which were in full 

 bloom was estimated at 2^2%. 



As the young fruit develops it seems to get more tender, until it grows 

 beyond a certain size, when it seems to get hardier again ; so that the later frosts 



