CAUSE OF MOTION IN PLANTS. 125 



it from pressing on the plant, and weighing the whole, co- 

 vering the plant, and tying it close at bottom, I left it six 

 hours. The difference of the weight, when I took it out, was 

 half a grain; nor could I feel the least moisture on the pa- 

 per. On breaking off different branches, and blinding my 

 eyes, I was always able to discover the branch dismembered 

 from the other, proyided it had been so for half an hour, 

 from the moist feel of the leaves, that can be compared only 

 to the death-like touch of a dying person. Most plants Moisture 

 have this when in sickness, and I am persuaded when con- c . ai 'f ed b y 

 fined in stagnant air. I think I may therefore finish this 

 subject also, and say, that there is no sensible perspiration in 

 plants, and that I very much doubt whether there is even in- 

 sensible perspiration : if there is, it is most trifling. 

 I am, Sir, 



Your obliged servant, 

 Cowley Cott. AGNES IBBETSON. 



Aug. 20. 



Explanation of the Plates. 



Plate III, figs. 1, 2, 3, a sting of the nettle in its different Explanation of 

 states. Fig. 1, its perfect state, when placed in the solar the P lates « 

 microscope, and before it stings : z the bag of poison : x the 

 spiral wire. 



Fig. 2, the sting after the poison has been thrown to the 

 point : x the spiral wire contracted. This is not drawn up 

 at night, when the stings bend, but only when it is touched. 

 If however a mirror be held over them, the poison is thrown 

 up directly. 



Fig. 3, the sting of the nettle very much broken. 



Fig. 4, untwisted Indian grass greatly magnified, showing 

 the manner in which it is formed. This is the first grass fo- 

 reign or English, in which I ever found the spiral wire; but 

 I doubt whether it runs through the whole of the grass. 



Fig. 5, the awn of the grass. 



Figs. 6 and 7> the grass twisted. 



Fig. 8, a longitud; a) section of the leafstalk of the mi- 

 mosa sensitiva, the middle pa-t containing five cases full of 

 spiral wire, and e c extrem t containing only three. 



PI. IV, fig. 1, a leaf of the mimosa. 



Fig. 



