422 PHILOSOPHICAL TRANSACTIONS. [anNO 1788. 



when touched, it contracts, that side becomes shorter than the other, and con- 

 sequently the filament is bent towards the germen. I could not discover any 

 thing particular in the structure of that or any other part of the filament. This 

 irritability is perceptible in stamina of all ages, and not merely in those which 

 are just about discharging their pollen. In some flowers which were only so far 

 expanded that they would barely ^dmit a bristle, and whose antherae were not 

 near bursting, the filaments appeared almost as irritable as in flowers fully 

 opened; and in several old flowers, some of whose petals with the stamina ad- 

 hering to them were falling off, the remaining filaments, and even those which 

 were already fallen to the ground, proved full as irritable as any I had examined. 



From some flowers I carefully removed the germen, without touching the 

 filaments, and then applied a bristle to one of them, which immediately con- 

 tracted, and the stigma being out of its way, it was bent quite over to the oppo- 

 site side of the flower. Observing the stamina in some flowers which had been 

 irritated returning to their original situations in the hollows of the petals, I found 

 the same thing happened to all of them sooner or later. I then touched some 

 filaments which had perfectly resumed their former stations, and found them 

 contract with as much facility as before. This was repeated 3 or 4 times on the 

 same filament. I attempted to stimulate in the midst of their progress some 

 which were returning, but not always with success; a few of them only were 

 slightly affected by the touch. 



The purpose which this curious contrivance of nature answers in the private 

 economy of the plant, seems not hard to be discovered. When the stamina 

 stand in their original position, the antherae are effectually sheltered from rain 

 by the concavity of the petals. Thus probably they remain till some insect 

 coming to extract honey from the base of the flower, thrusts itself between 

 their filaments, and almost unavoidably touches them in the most irritable part: 

 thus the impregnation of the germen is performed; and as it is chiefly in fine 

 sunny weather that insects are on the wing, the pollen is also in such weather 

 most fit for the purpose of impregnation. It would be worth while to place a 

 branch of the Barberry flower in such a situation, as that no insect, or other 

 irritating cause, could have access to it; to watch whether in that case the an- 

 therae would ever approach the stigma, and whether the seeds would be prolific. 



The Barberry is not the only plant which exhibits this phaenomenon. The 

 stamina of Cactus Tuna, a kind of Indian fig, are likewise very irritable. These 

 stamina are long and slender, standing in great numbers round the inside of the 

 flower. If a quill or feather be drawn through them, they begin in the space of 

 2 or 3 seconds to lie down gently on one side, and in a short time they are all re- 

 cumbent at the bottom of the flower. The motions in Dionaea muscipula. 

 Mimosa sensitiva and pudica, are too well known to be mentioned here. A 



