468 



Because these cells die and partially collapse, they make possible the 

 elongation of the cells lying directly about the vascular bundle and rich in 

 water. They have elongated in an approximately radial direction, begin- 

 ning at the sheath of the vascular bundle (h) and have divided by parallel 

 cross-walls (w). Besides the actual place of injury, the parenchyma of 

 the fruit wall has also participated in the radial elongation (r) and only 

 the inner flesh remains normal. On the boundary between the normal and 

 the over-elongated tissue a formation of flat cork (/) began at the time of 

 the observation. Joining the corked internal spot, this forms a consistent 

 tough mass. 



vSimilar cork places are met with in pomes, such as apples. Here, too, 

 the blow from hail often causes no open wounds, especially in unripe fruit. 

 We find only depressed places, which later turn practically brown. The 

 depression is produced by the bruising of the parenchyma of the apple skin, 

 lying under the epidermis which has not been injured, and. as a result of 

 which, it has dried and split, usually in radial cracks. Here, as in the 

 tomato, the starch has been retained in the corked tissue, adjacent to the 

 hail wound, in case the apple was still green when struck by the hail. In 

 this case, irregular zones of cork cells in the form of an hour glass are 

 often developed later, which cut ofif the whole internal hail wound from the 

 healthy flesh of the fruit. 



Most significant are the bark injuries due to hail, which, in themselves, 

 as a rule, are of slight extent, but represent considerable damage because 

 of their frequency. So far as I have had opportunity of observing these 

 injuries in fruit trees, I have found that the disturbance in the tissue has 

 not been confined simply to the bruised place but has also spread laterally. 

 In hail wounds on the one year old twigs of the current year, on which they 

 cause relatively the most considerable injury, the disturbance spreads later- 

 ally from the actual place of injury in the form of a softening of the bark. 

 As a result of this wc see, in cross-section, stripes of parenchyma extending 

 from the dead zone outward, and usually filled with starch, pushing into 

 the normal wood and softening it. It thus acquires brittle and crumbly 

 properties, which may be of special importance in those trees whose twigs 

 are used as tying and braiding materials (willows and birch). Wounds, due 

 to hail, may often be distinguished from the injuries due to frost by their 

 position in the annual ring. Since hail usually occurs in the hot season, the 

 wounds lie near the end of the annual ring, while frost injuries appear in 

 the spring wood. It is striking that beneath the places hit by hail in the 

 twig of the current year's growth, upon which frost cannot have acted at 

 all, one finds at times in the radius of the wounded place, that the pith is 

 browned and the spiral vessels greatly discolored, since the wood of the 

 vascular bundle, lying between the injury and the pith crown, is healthy. 

 The only possible conclusion is that the disturbance extends back toward 

 the pitli through the medullary rays. 



