4i8 



PLANT RESPONSE 



instance the maximum rate was as high as '0035 and the 

 minimum as low as *ooio mm. per minute. Confining our 

 attention to the uppermost of these series (c\ we find that 

 the responsive elongation is very quick, and the recovery 

 slow and incomplete. The average period of a single pulse 

 is twenty seconds. The results of series (c) are given in the 

 following table: 



Table showing Pulsations of Growth 



It will be seen from this table that the total growth 

 in eighty seconds is '0047 mm., giving an average rate of 

 growth of '003 5 mm. per minute. Had a magnifying 

 arrangement not been used, this average rate of growth, 

 shown by the dotted base line, would have appeared as con- 

 tinuous growth. By the magnification of the responsive 

 curve, however, we are enabled to see that such a rate is in 

 reality made up of numerous fluctuating growths of which it 

 is an average. 



Growth-response and excitatory response.— If we 

 compare these multiple growth-responses with the multiple 

 mechanical responses of Biophytum (fig. 116), their similarity 

 is at once evident. As in that case, so here also, recovery is 

 not complete, and the series of effects produced is therefore 

 additive in both cases. With Biophytum^ however, when 

 the leaflet is depressed to the utmost, a limit is reached ; 

 but in growth there is no such limit, and the summation 

 of effects may go on indefinitely, until senility and death 

 supervene. 



