EVAPORATION AS A CLIMATIC FACTOR. 57 



earliest are the hardiest, but those that are the least hardy have the most 

 moisture. 



The President — I would like to ask whether the subject does not 

 bear directly upon what we call winter freezing. That is, the freezing and 

 cracking of the trunk of a tree, which occasionally takes place, and which 

 to me has always been inexplicable. Isn't that a part of this problem 

 exactly ? 



Mr. Macoiin — Yes, the freezing does this. Thus, in the Province 

 of Nova Scotia, and I believe in a few places in New York, they have 

 been troubled with what they call crown rot of a tree. That is the 

 breaking away of the bark right at the base of the tree. In investigating 

 this, I have come to the conclusion that that is almost entirely due to the 

 late growth of the tree, and is due to the sudden breaking away of the 

 bark of the tree, owing to the fact that right at the base of the tree you 

 v/ill have the most amount of moisture in the trunk. The first fall of 

 snow prevents the drying out of moisture from that part of the trunk. 

 That snow may go away and then there may come a drop of tempera- 

 ture to 30 or 40 degrees below, and the cracking takes place. In those 

 parts where they adopt the highest method of cultivation, they are 

 troubled the most. The late growth is the trouble. 



Dr. Hansen — That must be the same trouble which we call "bark 

 bursting." That occurs in nursery stock out in the northwest. The 

 trunk becomes perfectly saturated with moisture, and it seems to fracture 

 the bark at the surface. I did not mean in my former remarks to ad- 

 vocate late cultivation. I meant if we had a late fall we should give the 

 trees a thorough watering before winter sets in. 



Mr. Macoun — I notice that Professor Watkins advocates cultivating 

 right up to the time winter sets in for hoed crops. I wrote to him but 

 did not get any reply from him. 



Dr. Hansen — One of our orchardists in Minnesota recommends the 

 cultivation of orchards right up to winter when the snow comes, but what 

 he means is not what we mean by cultivation. He simply means the use 

 of a disk harrow to scratch the surface and keep in the moisture. 



Mr. Von Herf — I have also had some personal experience in regard 

 to plums, apples and peaches, and also grape-vines in North Carolina. 

 The trouble does not occur every year, but it occurs in some years, some- 

 times being very disastrous. Sometimes hundreds of thousands of trees 

 will be killed. I know of only one year, however, when grape-vines 

 were killed in that way. Some were killed in the ground and others 

 sprouted out, but were killed dead. We found the stopping of cultivation 

 at certain times in the fall is a good precaution against this trouble, be- 

 cause we do not think it necessary of late to cultivate after the tree has 

 made its growth. We think it is for no purpose. We stop cultivating 

 about August. In regard to transplanting the trees, I have also some 

 experience and I can corroborate what Mr. Siebrecht says, that the trans- 

 planting of evergreens is most successful just at the period when they 



