432 



PLANT RESPONSE 



in the course of 50". The average period has thus fallen 

 from 12-5" at 34 C. to 5" at 44 C. The amplitude of pul- 

 sation at the same time is found to be decreased, and this, 



with the fact that recovery 

 is now complete, accounts 

 for the resultant cessation 

 of growth. 



Comparison of vari- 

 ous types of multiple 

 response. — At this point, 

 it is worth while to com- 

 pare two or three types 

 of multiple response. In 

 Bioftkytum we have seen 

 that, by reason of incom- 

 plete recoveries from nega- 

 tive turgidity- variation, 

 the multiply-responding 

 leaflet gradually becomes 

 depressed below its ori- 

 ginal level. In contrast to 

 this we have in growth- 

 response those incomplete 

 recoveries from positive 

 turgidity-variations which have the effect of gradual elonga- 

 tions In the pulsation of Desmodium again we have an 

 intermediate instance where, response and recovery being 

 equal, the responding organ is ultimately neither raised nor 

 depressed. It is interesting to note, therefore, that in raising 

 the temperature of a growing organ to the maximum, and 

 thus abolishing the resultant elongation, we bring on a con- 

 dition of equality of response and recovery which in so far 

 resembles the pulsation of Desmodium. 



Effect of external tension on growth. — Great advan- 

 tages are afforded by the method of magnified record, which 

 enables us to detect instantly the immediate and after effects 

 on the specimen of any changes of external conditions. It is 



Fig. 



176. Growth-pulsation seen in 

 Seedling of Balsam 



Upper record shows slow pulsations with 

 incomplete recoveries at 34 C. Lower 

 record shows quickened pulsations with 

 complete recoveries at 44 C. The 

 magnification employed is 500 times. 



