OM THE MECHANISM OF FLOWERS, g3 



fcack. It seldom falls quite off. It is curious, that the 

 Species of swivel, which belongs to it, is common to plants 

 ih general ; but is so contrived, that the part, within which 

 it turns, is but three quarters of a circle, see fig, 5, so that 

 if with the finger you turn the hood quite down, it comes oft". 

 The same piece of mechanism is foundin the phaseolus leaf, 

 and in many flowers. It is inconceivable what a perfect 

 weather glass this flower is': not a cloud can pass over the 

 sun, that does not change its position ; and every night the 

 whole flower is drawn up close, and shelters itself under the 

 leaves. 



The next flower, which I shall consider, in some measure Mechanism of 

 resembles the last, being a diadelphian, the phaseolus vul- * P ^ 

 garis. Here the principal contrivance is the contracting 

 of each part to the form of the pistil, by the means of the 

 spiral wire. The wings are moulded in the same model, 

 so that by drawing the spiral wire tight, it must necessarily 

 slip off the part on which it is placed; and by this means 

 throw itself to a certain distance from the body of the flower. 

 In its perfect state, fig. 6, gg, PI. IV, is fastened on to 

 h h, figs 7) 8 : of course, when the top of g^ is contracted 

 it will push off h h, by which means the flower opens to the 

 sun, and sends back the banner fig. 9 ; wliich contracting 

 in its turn by the means of two plaits under the collar ii, 

 it can wave itself backward and forward to admit the sun, 

 or to shade the body of the flower from it. In the same 

 manner the part^g-, fig. 6, by contracting, fills it up, and, 

 drawing the side which projects, almost turns the wings 

 round, and throws the banner at a distance, leaving the 

 pistil to twist till the keel w, figs 7 and 8, is broken, which 

 exposes the female to the sun. Then the usual process 

 takes place. I have observed, that, when the phaseolus Difference in 

 grows in a hothouse, the keel generally breaks; but it * hothouse. 

 appears, that the temperature \z not high enough, to 

 produce this effect in the open air in this country : we pro- 

 perly therefore can trust the indigenous flowers only, to 

 teach us to understand the real motion of a flower, Na- ' 

 ture certainly intended the keel to break, and expose the 

 pistil to the sun's influence, while the drops appear on it : 

 as the keel generally slips off from most of the 'diadelphian 

 G 2 plant« 



