6o9 



ish, extensive spots in the bark which have dried on the wood. In smooth 

 barked trees, instead of large, connected bhghted surfaces, numerous small 

 depressed places in the bark are noticed, appearing often on one side of the 

 tree. These resemble finger marks and are usually called frost plates. 

 These injuries are abundant, or scarce, according to the susceptibility of 

 the variety to frost and the conditions of the places of growth. In stone 

 fruits, the phenomena of blight are found most frequently in cherries and 

 plums; in the more sensitive peaches and apricots, the trunk usually suffers 

 as a whole. 



In pomaceous fruits, pears undoubtedly tend most easily to injuries 

 from bHght. Of forest trees, the beech and oak count as especially sensi- 

 tive and in damp places the ash and acacia also. The edible chestnut is 

 found in central Germany only in isolated localities. Among conifers, the 

 fir seems more sensitive to frost than the spruce. The larch suffers as soon 

 as it lacks sufficient light and air. The hnden and maple are rarely found 

 to be injured. Blight spots are found most rarely in the older birch, elm, 

 willow, poplar, hornbean, and especially the pine. 



The dying of the bark is to be considered as a direct effect of frost. It 

 penetrates to different depths and can, accordingly, produce a different 

 appearance in the different blight wounds. Thus, for example, frost fre- 

 quently attacks only the youngest layers of the bark and sap wood, includ- 

 ing the real cambium. The older, outer layers of the bark die only from 

 lack of nourishment, since the bark, killed by frost, turns dark in a short 

 time after thawing. We find in the spring (especially in pears) depressed, 

 sharply outlined places, often only very small in extent and at first only on 

 different sides of the trees, or branches. These places soon become dry 

 and adhere to the wood (Fig. 145 p). They are the above-mentioned 

 "frost plates" found by many fruit tree growers. A cleft appears at the 

 boundary between the dried part of the bark and the healthy part, which is 

 raised up by the growth in thickness of the trunk. The dead part of the 

 bark is again cut off from its surroundings by this cleft and loses its ar- 

 resting influence (Fig. 145 r). 



The arrestment, exerted by such a dead place, lies in the increased 

 pressure of the bark mantel so long as this bark mantel is still connected 

 with the dead, dry, inelastic tissue. The bark pressure will be greatest 

 near the dead places and the number of newly formed elements the 

 smallest. 



We find this at the beginning of the healing processes. The tree en- 

 deavors to cover the dead places by the formation of overgrowth edges 

 from the healthy parts of the bark. This can take place in two ways, 

 according to the kind of blight injury. If the branch, at the time of the 

 frost, already has some older wood, which is browned on the blighted side 

 but not split off, then the overgrowth edges often gradually push between 

 the dead bark and the wood body and slowly lift the scale-like, dry 

 brown mass of the bark. With each successive year, the overgrowth edges 



