Killing of Plant Tissue by Low Temperature 



199 



Table 19. Showing Effect of Slow Drying out on Hardiness 



OF Peach Buds in Winter. 



Variety 



Barnes. . . . 

 Barnes. . . . 

 Barnes. . . . 

 Connolly. . 

 Connolly. . 

 ConnoUv. . 

 Hills Chili. 

 Hills Chili. 

 Hills Chili. 



Buds From 



Date 



Girdled branch Jan. 14, '11 



Cut off branch Jan. 14, '11 



Check, normal branch Jan. 14, '11 



Girdled branch Jan. 14, '1 1 



Cut off branch Jan. 14, '11 



Check, normal branch Jan. 14, '1 1 



Girdled branch Jan. 14, '11 



Cut off branch Jan. 14, '11 



Check, normal branch Jan. 14, '11 



Number 



of 



Buds 



Average, Girdled branch 



Average, Cut off branch 



Average, Check, normal branch. 



321 

 275 

 325 

 198 

 281 

 217 

 501 

 351 

 465 



Percent- 

 age 

 Killed 



19.3 

 29.5 

 86.0 

 68.7 

 68.0 

 89.9 

 11.4 

 18.0 

 45.2 



33.1 

 38.5 

 73.7 



It is plain that this slow loss of water in case of winter resting 

 fruit buds has increased the resistance of the tissue to low tempera- 

 ture. 



Rate of Freezing. Pfeffer^ makes the following statement with 

 reference to the rate of freezing: "Resistant plants withstand 

 rapid and slow cooling equally well, and it is doubtful whether a rapid 

 fall of temperature is more injurious to plants killed by freezing 

 than is gradual cooling. That the injury is not due to the sudden 

 formation of ice after sub-cooling is shown by the fact that a peeled 

 potato is killed by freezing, although no sub-cooling occurs and the 

 ice forms gradually at -1 C, the freezing point of the sap." How- 

 ever, lately Winkler^, working with Pfeffer, finds that with winter 

 twigs that on cooling rapidly to -22 C. will be killed, if they are kept 

 for three days at -16 C, two days at -18 C, three days at -20 C, 

 two days at -22 C, three days at -25 C, and twelve hours at -30 

 to -32 C, they were not all killed. 



The rate of temperature fall is very important indeed, especially 

 in case of winter buds. In fact apple buds can be frozen in a cham- 

 ber surrounded by salt and ice rapidly enough that practically all 

 of them will be killed at a temperature of zero F., or slightly below, 

 while it is well known th.d they may go through a temperature of 



'Phys. of Plants. Eng. Trans, by Ewart, Vol. 2. p. 23.'>. (Hlbl. No. 88). 

 'Jahrb. f. Wis.s. Bot. Vol. 52. 1013. pp. 4n7-.'>n0. (lUbl. No. 121). 



