LONGITUDINAL RESPONSE OF RADIAL ORGANS 7J 



the cessation of stimulus ; and recovery was completed after 

 a further period of one minute. In this case the responses 

 exhibited fatigue. It may be stated here that, speaking 

 generally, the period required for recovery is dependent on 

 the strength of stimulus. With moderate intensity of 

 stimulation, recovery is complete within a comparatively 

 short period. But it is protracted, or indefinitely delayed, 

 when the stimulus is strong. Again, if successive stimuli be 

 applied, before recovery is complete, the responses will be 

 found to be additive. 



In order to convey some idea of the amount of contraction 

 produced by stimulus, I shall here give a detailed account of 

 an experiment on longitudinal contraction, the specimen 



Fig. 37. Response of Stem of Cuscuta to Electric Stimulation 



used being a young stem of the species of Bindweed 

 {Convolvulus) already referred to. The length experimented 

 on was 5 cm. On passing through this tetanising shocks 

 of five seconds' duration, a maximum contraction was 

 found to occur in the course of two minutes. The magnifi- 

 cation used for record was fifty times, and the extent of 

 contractile response recorded was 7*5 cm. Hence, the 

 actual contraction was 1*5 mm., in a stem whose length 

 was 50 mm. The contraction produced is thus 3 per cent, 

 of the original length. 



Similar contractile response may be obtained with other 

 forms of stimulation, and I shall now describe that induced 

 by thermal stimulus, the specimen used being the radial 



