.)_' 



Tlic al)iiii<l;iiil litci'jit ui'c on wiiilcr liai-diiicss, wliicli wc 

 do not Ircnt in dclnil, is somclinu's snrainarizcd in llio 

 statement thai, in JHicif plant i issues, death occurs Avlien 

 the temperatnic diops a few degrees below zero, while in 

 conifers and several otlnr crergreeiis the death tempera- 

 tures are lower by some 10, 20 or more degrees. Some 

 investigations, however, like the following one by Winkler 

 seem to indicate tliat llic ])r()hh'm is not so simple, there 

 being important seasonal variations in the same species. 



Winkler (1913) experimented on the cold resistance of 

 hiids, leaves, cambium, cortex and wood of branches, 5 to 6 

 years ohl, of nnnicrons species of trees. The branches 

 were cut into ])ieces 20 to 25 cm. long, split longitudinally, 

 and placed upright in a brass cylinder, with their lower 

 ends immersed in tap water in a glass dish set into the 

 bottom of the cylinder. The brass container was lowered 

 into an ice-salt bath and the temperatures recorded by a 

 thermometer suspended in the air between the twigs. 

 Subcooling was avoided by jjlacing a few ice crystals in 

 the water in the dish. After having been exposed for 12 

 hours, the material was thawed and its vitality investi- 

 gated by plasmolysis. The results were as follows: 1. In 

 experiments made in the Spring, the buds of 28 species of 

 deciduous trees, exposed to - 3°, were found uninjured, 

 only those of Quercus pedunculata having been killed at 

 that temperature; at -5°, all the buds were killed. Simi- 

 larly, the leaves or needles of 13 out of 14 species of ever- 

 greens were killed at approximately -4°. The cambium, 

 cortex, and wood of all the trees experimented upon sur- 

 vived exposure to -10°, but were all killed after 12 hours 

 at - 18°. 2. In the Summer, the cold resistance of decidu- 

 ous trees drops considerably, the death point of the cam- 

 bium, cortex and wood lying at about - 9°, while the resis- 

 tance of the same tissues in the evergreens undergoes 

 little change. 3. In the Fall, the resistance is on the up- 

 grade again, and it was found that in November, all the 

 buds of both deciduous and evergreen trees withstood 

 -17°, while those of 17 out of 29 deciduous trees, and 5 



