FUNCTION.] SPIRTING CUCUMBER. 157 



of the flower-stalk being less than the resistance of the 

 bract, it cannot be pulled back again by any power of its 

 own. After flowering, the flower-stalk becomes more woody 

 and stronger, and this is able to recover itself if it catches 

 against the edge of the bract, which is, however, not likely to 

 happen, because it is raised upwards beyond contact with 

 that organ. 



In conclusion, M. Morren compares the mechanism which 

 causes the apparent catalepsy of Physostegia to the escape- 

 ment of a watch, where a hooked lever stops the wheel, and 

 regulates the movements. 



To mere mechanical action ought also, perhaps, to be 

 referred the curious phenomenon well known to exist in the 

 fruit of the Elaterium, or Spirting Cucumber. In this plant 

 the peduncle, at a certain period, when the fruit has attained 

 its perfect maturity, is expelled, along with the seeds and the 

 mucus that surrounds them, with very considerable violence. 

 Here, however, endosmose appears to offer a satisfactory 

 explanation. According to Dutrochet, the fluid of the 

 placentary matter in this fruit gradually acquires a greater 

 density than that which surrounds it, and begins to empty 

 the tissue of the pericarpium : as the fruit increases in size 

 the same operation continues to take place ; the pulpy matter 

 in the centre is constantly augmenting in volume at the 

 expense of the pericarpium ; but, so long as growth goes on, 

 the addition of new tissue, or the distension of old, corre- 

 sponds with the increase of volume of the centre. At last 

 growth ceases, but endosmose proceeds ; and then the tissue 

 that lines the walls of the central cell is pressed upon forcibly 

 by the pulp that it encloses, until this pressure becomes so 

 violent that rupture must take place somewhere. The 

 peduncle, being articulated with the fruit, at length gives 

 way, and is expelled with violence ; at the same time the 

 cellules of tissue lining the cavity all simultaneously recover 

 their form, the pressure upon them being removed, and 

 instantly contract the space occupied by the mucous pulp ; 

 the consequence of which is that it also is forced outwards at 

 the same time as the peduncle. It has been found by 



