Researches on Growth and Movement in Plants. 379 



intervening distance be long or semi-conducting. Hence moderate stimulus 

 applied at a distance gives rise only to positive response ; direct application 

 of strong stimulus gives rise, on the other hand, to the normal negative. By 

 employing the electric method of investigation, I have obtained with ordinary 

 tissues the positive, the diphasic, and the negative electric response, in corre- 

 spondence with the responses given by a motile organ (fig. 7).* The 

 mechanics of propagation of the positive and the negative impulse are 

 different. It is therefore necessary to distinguish the quick transmission of 

 the hydro-positive impulse from the slow conduction of the negative impulse 

 due to the propagation of excitatory protoplasmic change. 



6. Effect of Indirect Stimulation on Growth. 



I will now describe certain remarkable phenomena connected with growth, 

 the discovery of which was due to the clue obtained from the characteristic 

 response to indirect stimulation that has just been described. I may say 

 here, in anticipation, that the results of experiments which I have carried out 

 on growth- variation under indirect stimulation are precisely parallel to those 

 obtained with non-growing organs. The effect induced by feeble stimulus 

 applied at a distance from the growing region is a positive variation or 

 acceleration of growth, which becomes negative, i.e., retardation of growth, 

 when the stimulus is applied at the responding region of growth ; under 

 intermediate conditions, the growth-variation is diphasic, a positive accelera- 

 tion followed by a negative retardation. 



Eocpt. 6. — Out of these three cases I shall give a detailed account of an 

 experiment relating to the positive variation of growth under moderate 

 indirect stimulation, since this particular case may have some important 

 theoretical significance. I took for experiment a growing bud of Crinum 

 and determined the region of its growth activity ; lower down a region was 

 found where the growth had already passed its maximum, and may there- 

 fore be regarded as an indifferent region. I applied two electrodes on this 

 indifferent region, about 1 cm. below the region of growth. On applying a 

 moderate electric stimulus of short duration, the response was an accelera- 

 tion of growth which persisted for nearly a minute, after which there was a 

 resumption of the normal rate of growth. In this particular case the-, 

 interval of time between the application of stimulus and the responsive 

 acceleration of growth was 12 seconds. The interval varied in different cases, 

 from 1 second to about 20 seconds, depending on the intervening distance 

 between the point of application of stimulus and the responding region of' 



♦ Cf. 'Plant Response,' p. 512 ; 'Comparative Electrophysiology,' p. 62 ; 'Irritability 

 of Plants,' p. 176. 



VOL. XC. — B. 2 H 



