THE RECORD OF GROWTH-RESPONSE 



417 



vigorously growing peduncle of Crocus which brings out in 

 an interesting manner the mechanics of growth (fig. 169). 



Rhythmic growth-response. — We saw that when the 

 sum total of energy is above par, a tissue becomes self- 

 excitatory in a multiple or rhythmic manner, giving rise 

 to periodic turgidity-variations. There may thus be respon- 

 sive pulsations of increased turgidity, each followed by 

 slow recovery from 

 such excess. With 

 each such pulse, a 

 transient elongation 

 of the growing tissue 

 will be produced, and 

 the succeeding slow 

 recovery will be more 

 or less incomplete. 

 This incompleteness 

 is due to the deposit 

 of material which 

 fixes growth. The 

 irreversible or per- 

 manent growth-effect 

 produced by each 

 pulsation, will thus 

 be measured by the 

 responsive elongation 

 minus the recovery. 

 This is well illustrated 

 in fig. 169, where 



Fig. 169. Multiple Growth-responses 

 (Peduncle of Crocus) 



The ordinate represents the extent of responsive 

 elongations in mm. ; the abscissa, time in 

 seconds. 



three separate sets of 

 responses are given, 

 taken from a single specimen in the course of the day. 

 Growth, as will be shown, is not uniform throughout the 

 day, but exhibits variation, in consequence of changing 

 conditions, such as that of temperature. But for a short 

 interval of time, the rate of growth under a constant en- 

 vironment, it may be taken as uniform. In the present 



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