168 EXPERBIENT STATION. [Jan. 



resistance, whereas plant tissues show a greatly reduced resist- 

 ance when heated. 



Our numerous experiments in subjecting seeds to electric cur- 

 rents have shown that when they have been soaking in water for 

 some hours and are quite moist, and a relatively strong current 

 is passed through them, the resistance is largely decreased 

 owing to the development of heat, and the current increases very 

 perceptibly. This also occurs to plants when subjected to cur- 

 rents of electricity of sufficient intensity, as it induces heat. 

 The injury caused to plants by electricity generally arises from 

 decreased resistance, which is likely to follow after a more or 

 less prolonged application of the current ; in other words, the 

 injurious effect is caused by heat, although it is possible that 

 electricity will kill plants without generating heat sufficient to 

 injure the j^rotoplasm. 



Experiments made some years ago by us seemed to indicate 

 that wdien strong currents are applied to small plants and they 

 become excessively heated, after a short period of time the pro- 

 toplasm is destroyed, and the current, which first increases in 

 strength very rapidly, suddenly drops to almost nothing. 



A low temperature in trees gives rise to a high resistance, and 

 a high temperature to a low resistance; in other words, the re- 

 sistance of trees resembles that of moist seeds in their behavior 

 to temperature, and the relationship between temperature and 

 resistance is quite general. There may be, of course, other fac- 

 tors which influence resistance besides temperature, such as, for 

 example, the degree of moisture in the tissue, as well as the 

 nature of the substances in the tissue. 



The relationship existing between temperatures and resistance 

 is shown in Figs. 1, 2 and 3. Fig. 1 shows the curve given by 

 an elm tree, and is based upon the data given in Table II., being 

 the average daily resistance obtained from the north, south, east 

 and west sides of the tree during April, the upper curve with 

 broken lines being that of the mean temperatures for the days 

 when the observations were made. In Fig. 2 A the average elec- 

 trical resistance of the south side of a maple tree is shown from 

 the data given in Table VITI. The readings are averages of 

 three daily readings at 8 a.m., 12 m. and 4 v.m., and in B is 

 given the average electrical resistance of a maple tree from data 



