344 BIOLOGY. [Book v. 



dui'ing the day, Do Candolle has seen flowers, habitually diumal, 

 open in the evening and shut in the morning. Flowers of 

 nocturnal habits changed also inversely.' 



Movements of the stamens are also common and generally 

 more rapid than those of the petals. The best known are those 

 of the stamens of the berberis vulgaris. When irritated by any 

 kind of contact, these stamens bend towards the pistil, and 

 scatter their pollen upon the stigma ; after which they stand 

 upright again, and approach the petals. The movement of the 

 stamens is sometimes spontaneous and successive ; thus Humboldt 

 has seen the stamens of the Pamassia palustris approach each 

 other one by one, and by jerks of the pistil, scatter their pollen 

 three times over the stigma, and resume their first position. 

 Certain venomous substances abolish these movements of flowers. 

 Flowering branches of species having petals or mobile stamens 

 are paralysed, when their stems are plunged into various solutions 

 (prussic acid, water of bitter almonds, alcohol, ether, acetic acid, 

 ammonia, &c.). The movements stop as soon as the venomous 

 liquid, by absorption, reaches the mobile organs .^ 



When once fecundation is accomplished, the vitality of the 

 flower diminishes, and the movements cease. 



Many plants have leaves which execute each day a regular and 

 periodical movement. They have a diurnal position, a nocturnal 

 position, and pass slowly from one to the other. Moreover, 

 certain of them are excitable by various contacts, mechanical 

 agents, light, &c., so that accidental movements are superadded 

 to the dim-nal movements. It is peculiarly in the leguminous 

 plants, especially the mimosas and oxalidese, that the slow move- 

 ments of wakefulness and slumber are most easily observed. 

 They are caused by the variations of the luminous intensity, and ' 

 are specially due to the action of the most refrangible rays.* 

 The species most celebrated for the mobility of their leaves 



' Memoires prisentes k I'lnstitjit. 



' Goeppert, De acidi hydroeyanici m m ptantis comvuntatio. Bresjau, 1827. 



2 J. Sach'a, loc. cit., p. 1029-1031. 



