WHAT IS WINTER-KILLINC? 187 



turity, and has tried various methods of orchard treatment for the con- 

 trol of maturity. Methods which hasten the ripening of the wood cause 

 it to enter the winter with better protection against dryness. At the same 

 time they increase the water in the soil, and make it possible for the 

 plant to lose much more water without being seriously damaged. 



Combining the observation and conclusions of Nelson and Emerson 

 with my own, which have been drawn from native plants, the following 

 summary is obtained: 



1. The winter injury or winter-killing of woody plants is caused by 

 dryness. It is most frequent in dry soils, and in those most deeply frozen, 

 because the water supply is low, and in regions with a dry windy climate, 

 because the water loss is great. Where both conditions prevail, as on 

 the Great Plains, unusual precautions must be taken against winter- 

 killing. 



2. Winter-killing is greatly influenced by the time of maturity. Native 

 trees stop their growth and mature early as the result of long-continued 

 adjustment to winter conditions. Cultivated species are found to resist 

 winter dryness in direct proportion to the rapidity with which they mature 

 in the fall. Critical selection of resistant individuals and the use for 

 grafting of trees with extensive and deep root systems will do much to 

 hasten maturity and hence to diminish winter-killing. 



3. Winter-killing may be prevented or at least decreased by methods 

 which will increase or preserve the water supply in the soil, by methods 

 for hastening the ripening of the wood or by methods of decreasing the 

 water loss from twigs and branches. The methods suggested by Emerson 

 for hastening maturing serve also to increase and preserve the Water con- 

 tent of the soil. Thorough cultivation and in many cases the formation of 

 a dust mulch, offers the most feasible method of controlling the water. 

 The use of a fall cover-crop of short duration will force early maturity and 

 at the same time will not have a harmful effect in drying out the soil for 

 winter. If the cover is not cut or is cut and allowed to remain as a mulch, 

 the soil will be even better protected against drought. If it could be made 

 as practicable, the same results could doubtless be obtained by using a 

 mulch during the summer, raking this up in the fall to force maturity, 

 and spreading it again at the approach of winter as a cover. Little can 

 be done to decrease water loss from branches and twigs, except by indi- 

 vidual treatment, which is out of the question in commercial orchards. 

 Maturity can be hastened, however, by the choice of upland. North slopes 

 seem to be preferable to south slopes, though this is an advantage 

 due to late starting in the spring rather than to a difference of amount 

 of exposure during the winter. 



DISCUSSION. 

 Mr. Davidson: I think that is a royal good paper, but I have come to 

 the conclusion that in Hamilton county we must be very careful about 

 trimming or pruning during the winter. If we make a cut on a tree dur- 

 ing a bright, sunshiny day it will go right into the heart unless it is 



