246 K. \V. HEGNER. 



being distended several times may have been due in part to 

 injury from the needle and in part to the separation of the 

 branches from the rest of the plant. The latter seems probable 

 at least in the case of branch d. 



Experiment M. 22. This experiment was carried out with 10 detached bladders, 

 5 from each of 2 stems. Bladders may be handled quite roughly without their 

 becoming distended and all of these 10 were successfully detached in the compressed 

 condition. They were then distended with a needle. Forty minutes later 8 of 

 them had again become compressed and the remaining 2 had partially regained their 

 compressed condition. 



These results show that the processes of both distention and 

 compression occur in detached bladders. 



Compressed bladders may become distended in several ways 

 besides that of touching the valve with a needle. When pressure 

 is applied to either side of the walls of the entrance by squeezing 

 the anterior end of the bladder between the arms of a fine forceps, 

 thus opening the valve, the bladder becomes distended. Dis- 

 tension similarly occurs when pressure is applied antero-pos- 

 teriorly. Compressed bladders may also be made to distend by 

 puncturing one side with a needle thus allowing the entrance of 

 liquid from outside. 



The difference in the amount of liquid in compressed and 

 distended bladders is considerable. Five branches were selected 

 and 3 large compressed and 3 large distended bladders were 

 detached from each, dried on the outside with filter paper and 

 the contents withdrawn with a fine pipette. It was found that 

 the contents of the 15 distended bladders amounted to approxi- 

 mately 88 per cent, more than that of the 15 compressed bladders. 

 That is, when a bladder becomes distended it draws in a volume 

 of the outside medium equal to about 88 per cent, of that already 

 present. The process of distention is remarkably rapid and 

 therefore the outside medium enters with considerable force. 



The amount of suction caused by the expansion of the walls of 

 the bladder is indicated by the following experiments. Para- 

 mecia were killed with heat and placed at various distances from 

 the entrance; the valve was then touched with a needle. It 

 was found that specimens as far away as 2 mm. were easily 

 drawn into the bladder. A dead insect larva 2 mm. long was 

 dissected out of one bladder and gently pushed against the valve 



