288 GENERAL PLANT PATHOLOGY 



Strong winds increase the amount of transpiration, so that fre- 

 quently we find there is a balance established between the absorbing 

 root system and the transpiring leaf system, so that the amount of 

 foliage is determined accordingly. If the amount of water lost by 

 transpiration exceeds the amount absorbed by the roots the plant 

 usually succumbs. Happy trees are those in which the amount of 

 water available exceeds the amount transpired, while unhappy trees 

 are suffering physiologic drought through the action of the wind in 

 moving water faster than it can be supplied (Figs. 114, 115, 116). 

 Such trees are seen in planted specimens in Long Island, Nantucket 

 and along our seacoasts. With tornadic winds, trees are uprooted in 

 general and irreparable damage is done. 



The effect of lightning is a marked one, as a determining factor in 

 disease. Recently Jones and Gilbert^ have published a paper on the 

 lightning injury to potato and cotton plants. One case occurred in a 

 field at Monetta, S. C. in the summer of 1913. The cotton plants 

 were fully grown and after a severe electric storm on Aug. 3, all the 

 cotton plants were killed over an area three rods in diameter. The 

 leaves wilted, died and blackened, but remained attached to the plants. 

 The most pronounced effect, however, was on the stem and root system. 

 Other cases are cited of a similar nature in Europe and America. 



The action of lightning on trees is variable. The tree may be 

 scorched, it may be stripped of its leaves, it may be cleft longitudinally, 

 or, more rarely, severed horizontally. Sometimes the bark is stripped 

 from only one side, occasionally without a trace of burning: at other 

 times, it may be riddled, as by worms, with a multitude of Httle holes. 

 The lightning furrows may be single, double, oblique or spiral. If the 

 tree is inflammable a fire may be started. Such tall trees, as the big 

 trees of California, have been struck repeatedly by lightning and their 

 leaders broken and their tops stunted as a consequence. From early 

 times, there has been a current belief that certain trees attract the light- 

 ning, that others are not struck. The elder Pliny beheved that "Light- 



^ Jones, L. R. and Gilbert, W. W. : Lightning Injury to Potato and Cotton 

 Plants. Phytopathology, 5 : 94-101, with plate, April, 1915; Jones, L. R.: Light- 

 ning Injury to Kale. Phytopathology, 7: 140-142 with i fig., Apr., 1917;, 

 Stone, George E.: Electrical Injuries to Trees. Bull. 156, Mass. Agric. Exper. 

 Stat., Oct., 1914. 



