WINTER KILLING AND HARDINESS 263 



suggest that certain cultural treatments may be employed to increase 

 the hardiness of plant tissue. Rapid freezing is probably more danger- 

 ous than slow freezing to plant tissue because there is not time for the 

 plant to develop a greater water-retaining capacity; consequently it 

 loses a larger percentage of its moisture at a given temperature. Con- 

 trary to general belief there is little evidence that rapid thawing is more 

 injurious than slow thawing. However, this should not be taken to 

 mean necessarily that rapid thawing in bright sunshine is not more 

 injurious than slow thawing under cloudy conditions, since the increased 

 permeability accompanying increased light may have an influence. 

 Critical temperatures for a given species will vary considerably with 

 conditions. 



