Irritability. 205 



other such phenomena are familiar to every observer of nature. 

 It is probable, indeed, that a different effect is produced upon all 

 plants by day and night, although it is less visible in some than 

 in others , thus plants of corn, in which there is little indication of 

 sleep when grown singly, exhibit that phenomenon very distinctly 

 when observed in masses ; their leaves become flaccid and their 

 ears droop at night. These effects have been generally attributed 

 to the action of light ; and it is probable that that agent contri- 

 butes powerfully to produce them ; for a flower removed from 

 the shade will often expand beneath a lamp just as it will be- 

 neath the sun itself. De Candolle found that he could induce 

 plants to acknowledge an artificial day and night by alternate ex- 

 posure to the light of candles. There must, however, be some 

 cause beyond the light, of the nature of which no opinion has yet 

 been formed ; many flowers will close in the afternoon while the 

 sun is still playing upon them, and the petals of others will fold up 

 under a bright illumination. Spontaneous movements are far 

 more uncommon than those which have just been described. 

 In Megaclinium Falcatum, the labellium, which is connected 

 very slightly with the columna, is almost continually in motion. 

 In a species of Pterostylis shown me by Mr. Brown, I observed 

 a kind of convulsive action of the labellums. The filaments of 

 oscillatorias are continually writhing like worms in pain ; seve- 

 ral other confervas exhibit spontaneous movements ; the most 

 wonderful of all has already been described by Linnteus him- 

 self, in a former part, as the Hedysarum Gyrans. To this curi- 

 ous class ought, perhaps, to be referred the curious phenomenon 

 known to exist in the fruit of the Momordica Elaterium, the squirt- 

 ing 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, endosmoses (the 

 circulation of the sap) 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 takes place, the 

 pulpy matter in the centre is constantly augmenting in volume 

 at the expense of the pericarpium ; but so long as the growth 

 goes on, the addition of new tissue, or the distension of old, cor- 



