IRRITABILITY 



225 



- Compound leaf of Woodsorrel : 



Fig. 249. - 

 day-position. 



Fig. 250. — Ditto : night-position. 



certain plants {e.g. seedlings of the Sunflower and of Stellaria 

 media), which either rise or sink as night sets in. The 

 foliage-leaves of Stellaria media also move : at night the 

 opposite leaves at each whorl incline towards each other 

 with their tips pointing more or less towards the apex of the 

 249 250 stem : at daytime these 



leaves diverge and stand 

 out more nearly at right 

 angles to the stem. In 

 compound leaves the move- 

 ments of the leaflets are 

 even more striking. By 

 day the three leaflets of a 

 leaf of the Woodsorrel 

 {Oxalis acetosella) are fully 

 expanded and horizontal 

 (fig. 249); but at night- 

 time the leaflets droop 

 vertically downwards, something like a closed umbrella (fig. 

 250). The leaves of the Dutch Clover {Trifolium repens) are 

 expanded by day (fig. 

 251); but at night the 

 three leaflets composing 

 a leaf bend and fold so 

 that the terminal leaflet 

 forms a roof over the two 

 lateral leaflets (fig. 252). 

 The pinnate compound 

 leaves of many Legum- 

 inosae either rise or sink 

 at night-time, and the 

 opposite leaflets bend to- 

 wards each other in pairs 

 either upwards or down- 

 wards. 



Many flowers and some inflorescences have difl^erent day- 

 and night- positions. In most cases the flower or inflorescence 

 (usually capitulum) is open at daytime (fig. 253), but closed 

 by night (fig. 254); but each flower has its own opening and 

 closing time. The accompanying table shows the opening and 

 closing times of some flowers and inflorescences ; it also shows 



p 



Fig. 251. — Compound leaf of Clover : 

 position. 

 Fig. 252. — Ditto : night-position. 



day- 



