Researches on Growth and Movement in Plants. 



377 



give the record of a single pulse of growth obtained with the peduncle of 

 Crocus (fig. 6, h). The magnification employed was 10,000, the successive dots 



Fig. 6. — a, time-relations of response of growing bud of Crlnura to electric stimulus of 

 increasing intensity applied at the short lines ; h, record of a single growth-pulse of 

 Crocv^. 



being at intervals of 1 second. It will be seen that the growth-pulse 

 commences with a sudden elongation, the maximum rate being 0'4 yu, per 

 second. The pulse exhausts itself in 15 seconds, after which there is a partial 

 recovery in the course of 13 seconds. The period of the complete pulse is, 

 therefore, 28 seconds. The resultant growth in each pulse is, therefore, the 

 difference between elongation and recovery. Had a highly magnifying 

 arrangement not been used, the resulting rate would have appeared con- 

 tinuous. In other specimens, owing probably to greater frequency of pulsa- 

 tion and co-operation of numerous elements in growth, the rate appears to be 

 practically uniform. 



Table I. — Time-relations of Growth-variation under Electric Shock. 



Intensity of stimulus. 



Latent period. 



Normal rate. 



Ketarded rate. 



0-25 unit 

 1 unit 

 3 units 



6 seconds 

 4 seconds 

 1 second 



"62^4 per sec. 

 0-62 „ „ 

 -62 „ „ 



"49 /i per sec. 

 0-2o „ „ 



Temporary arrest of growth. 



It is thus found that growth in plants is affected by an intensity of 

 stimulus which is below human perception ; that with increasing stimulus 

 the latent period is diminished and the period of recovery increased ; that 

 the induced retardation of growth increases continuously with the stimulus 

 till at a critical value there is a temporary arrest of growth. 



