1882.] on tJie Excitability of Plants. 157 



sliown in tlie drawing, the style is not lipped but awl-shaped. It 

 reaches to the mouth of the showy, orange-coloured corolla, to the 

 inside of which it is united by its under surface. It has a smooth 

 side, the epidermis of which is made up of numerous small j)ris- 

 matic cells and is very elastic, and, in the unexcited state, concave, 

 and a papillated side beset with the nipple-like ends of cylindrical 

 cells, which, when unexcited, are distended with liquid. These 

 cylindrical cells are continuous with those of the conducting tissue 

 of the style. When an insect enters the flower, it does two things ; 

 it charges the fringe of hairs on the inside of the corolla with pollen, 

 and touches the style, which, in consequence, bends suddenly in the 

 opposite direction to that in which it was bent before, so as to plunge 

 its stigmatic surface into the fringe. In this motion the epidermis 

 acts as a spring simply. So long as the stigmatic tissue is turgid it 

 cannot act. The moment its cells lose their tension, off it goes.* 



Another plant investigated by Morren is one of very different 

 organisation, but is one in which the existence of excitability has an 

 equally plain teleological interjDretation. Long ago Robert Brown, 

 lo whom plant-lore owes so much, when exploring the flora of Botany 

 Bay, became acquainted with the now well-known Australian i)lant 

 called Stylidium.t [A specimen from the Royal Gardens at Kew was 

 exhibited.] Here is the plant (Fig. 4). The flower is too small to 

 be easily seen, but the diagram will enable you to understand the 

 mechanism. It has again to do with insects and fertilisation. In 

 Stylidium the anthers and stigma are united together at the summit 

 of a cylindrical stem which may be compared with the motor organ 

 of Mimulus. You might naturally suj^pose that they were arranged 

 so in order that the pollen from these anthers should be at once 

 received by the adjoining stigmatic surface. That it is not so is 

 evident from the order of development of the flow J , for you find that 

 at the moment that the anthers burst, the stigma is not yet mature. 

 Consequently the pollen is not intended for it, but for flowers which 

 have come to maturity earlier, and the mechanism which now interests 

 us fulfils this purpose. The figure shows the singular form of this 

 strange flower. You observe that the column, as it is called, is bent 

 down over the corolla so as to be in contact with the odd-looking 

 labellum, which here takes the place of one of the petals. At the 

 moment that the anthers burst the column attains its greatest 

 sensitiveness. The slightest touch causes it to spring up, straighten 

 itself suddenly, and then bend over to the opposite side. The 

 mechanism resembles that of Mimosa and of Mimulus. There is a 

 spring, the action of which is restrained by the resilience of cells 

 distended with liquid. Suddenly these cells discharge their contents 

 and the spring acts. ' 



* '' Kecberches sur le mouvement, &c, du style du Goldfussia anisophylla " 

 Mem. de FAcad. Eoyale de Bnixelles, 1839, vol. xii. '^upuyua. 



t Morren, " Ee'cherches sur le mouvement et I'anatomie du RtvbVlinni 

 granuiiifulium." Mem. de I'Acad. de Bruxelles, t. xi., 1838 stylidium 



