IRRITABILITY OF PLANTS. toa 
phenomenon. Perhaps it is in some manner 
connected with the very peculiar vegetable 
function of which we are now about to speak. 
This is called irritability. There are many 
points in which a sort of similarity between 
plants and animals may be traced, such as the 
motion of their juices, their functions of respira- 
tion and digestion, and in the formation of their 
different tissues; but one point is denied to the 
vegetable world by almost universal consent—the 
power of motion. Perhaps we shall succeed in 
shewing that even this must now be given up, 
and that plants, in some instances at least, are 
really possessed with a notable, although limited 
power of moving their various organs. Indeed 
if we were to look at the very meanest plants, 
which are of a size only to become visible to the 
eye with the aid of the microscope, we might lay 
our finger on some which cannot be distinguished 
in many respects from minute animalcules, but are 
able to move about from place to place, yet in 
every other particular resemble plants. In the 
higher plants, such as trees, &c. we have nothing 
of this sort to tell of, from the reason that they 
are necessarily tied to a certain place by their 
