LONGITUDINAL RESPONSE OF RADIAL ORGANS 79 



lies in the fact that they necessitate only moderate intensities 

 of stimulation, which have the advantage of not fatiguing the 

 tissue. 



Modification of excitatory contraction by physiological 

 conditions. — That these contractions are the expressions of 

 true excitatory response is proved by the fact that they are 

 modified by whatever affects the physiological condition of 

 the tissue. Thus, for example, they undergo a temporary 

 abolition under the action of anaesthetics, and a permanent 

 abolition under the action of poisons. This will be demon- 

 strated in more detail in a later chapter. They also exhibit 

 very interesting modifications, according to the age of the 

 specimen and the season of the year, as might theoretically 

 have been expected. In experiments on this subject, under- 

 taken with the filamentous corona of Passiflora, stimulation 

 was produced by tetanising electric shocks, and the maximum 

 contraction was measured by means of a micrometer. The 

 following results show, in condensed form, the effect of age 

 on excitatory contraction. 



Table showing Effect of Age on Excitatory Contraction 

 (Coronal filaments oi Passijlora q.) 



[Length of specimens, 21 mm. Time, February, i.e. end of winter.] 



Age of Specimen. , •^';"°',".'' Mean Percentage of • 



contraction. 



contraction. 



Flower already opened -j (A) 1-5 mm. |- 1-51 mm. ' 7-2 per cent. 



One day before opening- (/^) 17 mm. ; 171mm. 8-i per cent 



i(a) , 1-65 mm. | 

 Bud . . . i((6) 1-6 mm. j- i -6 mm. 7-6 per cent. 



[(c) I -5 mm. ) 



It will thus be seen that when the physiological activity 

 of the specimen is at its greatest, that is to say, just before 



