

TRANSMISSION OF EXCITATORY WAVES IN PLANTS 249 



but the velocity of transmission was now found to be much 

 reduced. Instead of icri seconds being necessary for trans- 

 mission through the entire length, it was now found to take 

 148 seconds. The difference of 47 seconds here, represents 

 the additional time taken for transmission through the 10 mm. 

 length of cooled tissue. In other words, whereas transmis- 

 sion through 10 mm. of normal tissue had taken about 

 2'6 seconds, it now took about 2'6 4- 47, or 7*3 seconds ; that 

 is to say, the conductivity was reduced by cooling to nearly 

 one-third. 



Effect of rise of temperature on velocity. — It has been 

 proved that conductivity is reduced by lowering of tempera- 

 ture. We should therefore expect that a rise of temperature 

 would produce the opposite, namely, an increase of conduc- 

 tivity. That this is the case was shown by an experiment 

 on a leaf of BiopJiytinn. Care was taken that the leaf should 

 not be too young, since, as will be shown later, the effect of a 

 rise of temperature on a young leaf is to initiate automatic 

 response. I found that in this specimen excitation travelled 

 a distance of 41 mm. in a centrifugal direction in 11 seconds, 

 the temperature being 30 C. The velocity at this tempera- 

 ture was therefore 37 mm. per second. On now raising the 

 temperature to 35 C. the time taken for transmission was 

 reduced to half, i.e. 5-5 seconds. The temperature was next 

 raised to 37 C, and the time was now found to be further 

 reduced to 4*5 seconds, the velocity being thus 9/1 mm. per 

 second, or nearly three times as great as at 30 C. 



Table showing Effect of Rise of Temperature otf Velocity 

 of Transmission in Biophytum 



Temperature 



Distance 



