Some Hydration Reactions and Growth. 



157 



or below. As the temperature of the air rises above this point in the 

 morning, acceleration ensues and a high rate prevails until the ther- 

 mometer shows 25° C. or above, at which time retardation takes place, 

 which may continue to complete 

 cessation or even shrinkage. It was 

 noted that the behavior with respect 

 to the temperature in this region 

 might be modified by varsdng the 

 conditions of water-loss, and that 

 growth might be maintained at a 

 higher rate if high humidity around 

 the growing member is maintained. 

 As the temperature falls at the 



Fig. 41. — Diagram showing the elonga- 

 tion of four 1-cm. intervals into which 

 a young pod waa divided. Maximum 

 increase ensued in third centimeter 

 from base. 



Fig. 42. — Arrangement of auxograph to 

 take variations in length of pod of 

 Phaseolua. The mature tip of pod is 

 fastened to cork buffer on end of lever of 

 instrument. 



close of the day the rate accelerates again and growth is rapid until 

 checked by the falling temperature. (Fig, 43.) 



These records were all made of plants not subjected to the direct 

 action of the sim. One was placed in such position that the svmlight 

 fell directly upon the pod for about 15 minutes before 6 p. m., with the 



Fig. 43. — Tracing of auxographic record of growth in length of bean pod, X 45. The features 

 of active elongation are similar to those described for variations in thickness in fig. 44. 

 Retardation of growth is seen at temperatures above 30° C. Downward course of pen 

 denotes increase. 



result that a sudden enlargement followed, which was quickly retracted 

 and quiescence or slow shrinkage followed. Such sudden variations 

 have been seen in other types of organs, such as the joints of Opuntia, 

 and seem to be enlargements due to expansion of gases in the organ, 

 the cavity of the pods in this case being of such size that a marked 

 response might be expected (fig. 44). The features of variation of 



