24 



MASS. iiXPERIMENT STATION BULLETIN 226. 



to winter-killing in the severe winter of 1917-18 which injured many Bald- 

 wins and Rhode Island Greenings and a few Kings. Several trees among 

 the Baldwins, Spies and Kings were killed back to the snow line or 

 severely checked by killing the wood while the bark and outer thin shell 

 of wood remained alive. This doubtless interfered with the rise of water 

 and checked growth for a year or two. Where they were killed back to 

 the snow line a strong shoot arose in many cases and a good leader tree 

 resulted. 



The unpruned trees generally assumed a modified leader type and have 

 naturally developed rather thick tops with many branches coming oul 

 of the central trunk. 



Cutting back young trees is generally advocated, one object being to 

 secure low headed trees. In 1919 measurements were made of the height 

 of the lowest branches on these trees. The maximum difference between 

 the average of trees cut back at planting and those not cut back was only 

 about seven inches, a diflPerence that is of no significance in mature trees. 



An argument for cutting back frequently advanced is that it makes the 

 tree, including the cut back branches, more stocky. It is now generalh' 

 recognized that any increase in stockiness arises from shortening the 

 branch and not from increased diameter. In the fall of 1923 the four 

 largest branches on each tree of the Baldwins, Rhode Island Greenings 

 and Mcintosh trees were measured four inches from the trunk. The 

 relative size of these branches is shown in Table 2, the unpruned trees 

 being taken as 100. 



Table 2. Relative size of branches of trees receiving different types of 



pruning. 



It will be seen that cutting back the side branches has not increased 

 their diameter; but on the contrary, in all except the Mcintosh, they are 

 smaller on the cut back trees. The principal factor governing the size of 

 the main branches is their number. The fewer branches there are the 

 larger the four principal branches may grow; that is why all the pruned 

 trees (except the cut back leader Rhode Island Greening) have larger 

 main branches than the unpruned trees. It also explains why the four 

 largest branches on the globular trees are larger than those on the leader 

 trees; there are fewer additional smaller branches to compete. 



After the growing season of 1921, when the trees had completed nine 

 seasons growth, the height and spre;id of the trees were measured, and the 

 average of all varieties for the se\er;il methods of pruning is shown in 

 Table 3. 



