SHADE TREES. 



207 



bark was brought about by winter injury to the cork cambium, a vital 

 layer located between the outer and the inner bark. It did not injure the 

 tree in the least, since the inner bark and the cambium layer underneath 

 remained unaffected. As the collapsed cells of the cork cambium decom- 

 posed, the outer bark became loosened from the tree and fell off in a year 

 or two, covering everything it happened to fall upon with a peculiar red- 

 dish powder. A microscopic examination of this powder showed it to 

 consist of disintegrated cork tissue, or lamella-. This injury to cork cam- 

 bium from low temperature, although 

 observed here and there, was not common. 

 In one city in New York, however, 50 

 trees were affected, but in only one or two 

 instances did injury extend to the wood 

 and involve the cambium layer. One large 

 sycamore tree 4 feet in diameter, which we 

 observed, lost all of its outer bark, but is 

 in good condition at the present time. 

 The large section of bark, composed of 

 many annual layers of cork, fell off in a 

 comparatively short time, giving to the 

 trunk an unusual whitish appearance. 

 Occasionally there may be found in our 

 State elm trees in which the cork cam- 

 bium has been affected by winter tempera- 

 ture, resulting in a subsequent loss of the 

 outer bark. But the exfoliation of small 

 portions of the outer bark of elm trees 

 is not uncommon, and should cause no 

 apprehension. 



Sun Scald. 



Sun scald is a type of injury affecting 

 unripened wood. It is quite commonly 

 met with on rock maples and orchard 

 trees and on some of our wild slirubs. 



Shade-loving trees are particularly susceptible to sun scald, as may be 

 observed in any forest clearing. For instance, the moose maple, a shade 

 plant, seldom scalds in its native habitat, but when timber is removed 

 and the sun allowed to enter, it is affected. Tliis tree is undoubtedly 

 the most susceptible of any to sun scald. 



On the apple sun scald is often associated with canker {Spharopsis) . 

 White pines also, when tliinned too freely, will sun scald severely on the 

 trunk. Many shade trees in our State show injury from this cause, the 

 trouble being more common in some localities than in others. In one 

 section of a city in the eastern part of the State more than 60 per cent, of 

 the maples were found to be suffering from sun scald. The scars, which 

 were confined to the trunk, were invariably on the sunny side of the tree. 



Fig. 80. —Elm tree which lins lost 

 its outer l)ark, resulting from 

 winter injury to cork cambium. 



