On the Physiology of Vegetnlles. 183 



is the muscle of the plant, we shall find it in the great discovery 

 of HA1.1.ER, in stimnlating the muscles of animals by caustics 

 and sharp-pointed instruments: the spiral wire being equally 

 affected by both, retiring (if quite fresh and in health) from 

 the accession or touch of eith.er. 



By means tiierefore of the muscle of the plant throwing the 

 leaf into action, the leaves are most properly denominated lungs 

 to the plant. But this is not all the office of this part of the 

 vegetable. In the leaf is mixed that juice of tlie bark by che- 

 mical affinity which contributes to altering the colour of the 

 blood of the plant, so changing by means of the oxygen the dark 

 resinous thick blood into a fresher liquid of a more florid colour, 

 and thus reducing it also into a tliinner juice, which enables it 

 to run with speed down the inner bark vessels at the bottom of 

 the leaf, which lead directly down to the bark. The first part 

 of this is exactly what our lungs do ; and this alone would en- 

 able the resinous juice to flow with ease to the bark, when first 

 made in the leaves of the vegetable. 



I shall now turn to the third and last proposition I am to 

 give in this letter, which is equally new, and taken from the dis- 

 section of plants. It is "that the corolla of a JIoLver is formed 

 by bubbles of water placed in rows, and owes all the beauty and 

 lightness of its tints to the refraction and reflection of the sun 

 on the balls of water which compose its pabulum." 



The corolla, to be known, must be taken to pieces. There is 

 some art required to do this; for, if the petals are at all pressed, 

 they are destroyed ; thev soon break their bubbles and spill their 

 liquid, and thus spoil the whole specimen (as may be seen by 

 pressing one). But it is possible to take the petal of each dif- 

 ferent corolla, and, splitting it, draw off the upper and under cu- 

 ticle, and, leaving only tlie niidrlle part to be examined, " that is 

 the pabulum," to gain the most exact result; — since the dif- 

 ferent cntifles will then (if placed in the microscope) properly 

 so arrange themselves (according to their true and focal distance), 

 that, though there are several separate layers, yet they are so lit- 

 tle divided, each will rise to its proper height, and e/iuble the 

 eve to distinguish tiiem from each other, and not in any man- 

 ner confuse their jjarts together. Taking the corolla in this man- 

 ner, the i)al)ulum is soon discovered to be balls of water laid in 

 rows; and this even the naked eye in some flowers will show ; 

 and these l)ul)bles of water (covered only by an extremely thin 

 skin) lined by an impervious one, so clear as often scarcely to 

 appear to the naked eye. 



The petals of most (lowers differ from loaves in many respects, 



but particularly in one essential point:— in leaves, the coloured 



M 4 skin 



