Killing of Plant Tissue by Low Temperature 



28^ 



Not nearly so large a percentage of unopened as open bloom 

 was killed, as the following table will show: 



Table 48. Showing Percentage of Open and Unopened Bloom 

 Killed by the Freeze of April 4, 1908 



It will be seen that enough fully open bloom was uninjured 

 at this temperature, 24 F., for a good crop if the tree had a heavy 

 set of bloom. In fact a minimum thermometer that checked with 

 those of the U. S. Weather Bureau registered a temperature in the 

 Missouri Experiment Station orchard of 23 F., so in some years 

 at least, peach bloom may be expected to withstand a temperature 

 that low. 



Those three tables bringing out the facts, that the bloom just 

 before the petals open will withstand lower temperatures than fully 

 open flowers; that the flowers open more rapidly toward the tips of 

 the twigs, and that therefore flowers on the outer half of the twigs 

 are less likely to survive a spring frost coming before the bloom is 

 fully open, suggest that the tree should be pruned to a sufficiently 

 open head that the leaves at the base of the twigs will not be shaded 

 off before fruit buds are formed. 



The greater hardiness of unopened buds is apparently not due 

 to the protection of the petals. In freezing 59 unopened blooms 

 to a temperature of -3 C, 11.8 per cent of the pistils were killed 

 while of 50 unopened bloom with the petals and stamens removed, 

 no pistils were killed. 



On April 30, 1908, the temperature fell to 28 F. in Columbia. 

 The calyx tube was just breaking from the young fruit. The follow- 

 ing table gives the percentage of fruits kilkil at Columbia: 



