viii RESEARCHES ON IRRITABILITY OF PLANTS 



ideal methods of attacking problems in the life of plants, 

 the realisation of which would make a great advance in 

 physiological investigation. 



It would also be desirable to discard, if possible, the 

 troublesome method of obtaining record by photography, 

 which necessitates work in a dark room ; in this connection 

 it should be remembered that subjection of the plant to 

 darkness introduces compHcations by modifying its normal 

 excitability. For these reasons, another requirement which 

 it is necessary to fulfil is the devising of some simple and 

 direct method of obtaining the record. And in order that 

 the results obtained should not be influenced by any personal 

 factor, it would be further desirable that the plant attached 

 to the recording apparatus should be automatically excited 

 by stimulus absolutely constant, should make its own . 

 responsive record, going through its own period of recovery, 

 and embarking on the same cycle over again without 

 assistance at any point on the part of the observer. 



The difficulties encountered in realising these ideal 

 requirements appeared at first to be insurmountable. In the 

 records of response serious errors occurred as regards ampli- 

 tude and time-relations, owing to the friction of the writing 

 lever against the recording surface. As an extreme instance 

 of this, in recording the rhythmic movement of the leaflets 

 of Desmodium the very slight friction which the smoked- 

 glass surface offered was enough to stop the pulse-record. 



After many attempts, I was at last successful in 

 overcoming all obstacles by the device of the Resonant 

 and Oscillating Recorders. Taking the very difficult test 

 of direct record of the rhythmic movements of Desmodium 

 leaflets, it will be found that the pulsations recorded in this 

 book not only gave accurate measure of the amplitude and 

 period, but also the absolute rate of movement during any 

 phase of their autonomous response. Again, in the matter 

 of accurate measurement of short intervals of time required 

 for the determination of the latent period and velocity of 

 transmission of excitation, I have shown the possibility 



