MOTILE AND IRRITABLE PARTS OF PLANTS. 787 



ligulate florets of the capitula of many Compositae, as the dandelion, daisy, Tragopogon, 

 and many other Cichoriaceae, behave in reference to the whole inflorescence like single 

 petals, alternately approaching and receding from one another. 



(3) Many leaves endowed with periodic motility or sensitiveness to light are also 

 irritable to contact and concussion, as those of Oxalis Acetosella, stricta, corniculata, purpurea, 

 carnosa, and Deppei^, Robinia pseud-Acacia~, various species of Mimosa, as sensiti'va, pros- 

 trata, casta, 'vi'va, asperata, quadriualvis, dormiens, pernambucina, pigra, humilis, cind pe/Iita, 

 yEschinoniene sensiti'va, indica, and pumila, Smithia sensitiva, Desmantbus stolonifer, trique- 

 trus, and lacustris. In the greater number of these plants a rather violent or otten 

 repeated concussion is requisite to set the parts in motion, which then always assume the 

 position of sleep ; in other words, mechanical irritation acts in the same way as a dimi- 

 nution of light. This is the case also in Oxalis (Biophytum) sensiti'va and Mimosa pudica, 

 where however a very slight concussion or simple contact on the contractile organ suffices 

 to cause immediate and considerable motion, which is then conveyed, when the plant is 

 highly irritable, by conduction of the irritation to the parts not touched. 



Among irritable stamens may be enumerated the various species of Berberis^ (f-S- 

 vulgaris, eniargiuata, cretica, and cristata, and of the sub-genus Mahonia. In contact 

 with the corolla when at rest, they curve concavely inwards when the base of the inner 

 side of the filament is lightly touched, so that the anther comes into contact with the 

 stigma. 



There is a greater diversity in the phenomena produced by a slight blow or friction 

 on any part of the filaments of various Cynaraceae (as Centaurea, Onopordon, Cnicus, 

 Carduus, and Cynara) and Cichoriaceae (as Gichorium and Hieracium). The filaments 

 which spring from the tube of the corolla bear the five firmly attached (not coherent) 

 anthers, which together form a tube through which the style grows up while the pollen 

 is escaping. At this time the filaments are irritable ; when at rest they are curved con- 

 cavely outwards as far as the width of the corolla-tube will permit ; on contact or 

 concussion they contract, become straight, and hence come into close contact along 

 their whole length with the style which they enclose, lengthening again after some 

 minutes and resuming their curved form. Since each separate filament is independently 

 irritable, touching a single filament or a blow on one side only of the capitulum will irri- 

 tate, according to circumstances, only one, two, or three of the filaments, and by the 

 contraction of one side the whole of the reproductive organs will be bent to one side. 

 By the displacement connected with this or the pressure of the other filaments on the 

 corolla, they are also irritated, and thus arises an irregular oscillating or twisting motion 

 of the reproductive organs of the flower. If the whole capitulum is shaken, or if the 

 hand is passed over the surface of the flower, or the flower is blown into, a ' creeping ' 

 motion ensues of all the flowers in the capitulum. This phenomenon occurs only while the 

 style is growing through the anther-tube and the pollen is being emptied into the tube ; the 

 motion of the filaments effected by insects causes the anther-tube to be drawn downwards 

 and a portion of the pollen thus to escape above it, which is then carried away by insects 

 to other flowers and capitula where the stigmas are already unfolded'*. 



Among irritable female reproductive organs are the lobes of the stigmas of Mimulus, 

 Martynia, Goldfussia anisophylla, &c., which close when their inner side is touched, 

 evidently in order to retain the pollen brought to them by insects. More striking are 

 the movements which follow a light touch on the gynostemium of Stylidium, a genus 



^ From Unger, Anatomie und Physiologic der Pflanzen, 1853, p. 417. 



^ Mohl, Flora, 1S32, vol. II, No. 32, and his Vermischte Schriften. 



^ Goeppert, Linnaea, 1828, vol. Ill, p. 234 et seq. 



* These phenomena were discovered as long ago as 1764 by Count Battista dal Covolo, and are 

 well described by Kolreuter in his preliminary Nachrichten von einigen das Geschlecht der Pflanzen 

 betreffenden Versuchen; 3rd Appendix, 1766, pp. 125, 126. 



3 E 2 



