THE NERVOUS MECHANISM OF PLANTS 409 
at once suggests an action similar to that which they have 
on the nervous mechanism of an animal. When the effect 
of the fatigue or the anesthetic has passed off, the organ 
again becomes capable of responding. 
While we are able from these considerations to recog- 
nise in the plant a nervous system in some way com- 
parable to that of an animal, we must clearly recognise the 
limitations under which it exists. It can only be regarded 
as rudimentary and as showing a very slight degtee of 
differentiation. This we have seen is particularly notice- 
able with regard to its co-ordinating power. Another 
feature must be mentioned, however, before leaving the 
subject. We do not find in the plant any indication of 
anything corresponding to the higher functions of the 
nervous system of the higher animals. There is little evi- 
dence of anything which we may compare to consciousness 
or volition. Though many of the responses to stimulation 
are eminently purposeful we cannot regard them as in any 
way modified or held in check by any controlling power. 
A stimulus will produce its due effect although the mani- 
festation of that effect at the particular moment may be 
followed by injurious consequences. ‘The connection between 
the sense-organ and the motor mechanism is apparently 
a direct one, and there is no power to modify it possessed 
by the organism. 
Nor, so far as we know, have we in plants any power 
of initiative. True, there are many movements and 
changes which are set up by causes that have their origin 
in some alteration of the protoplasm which we cannot 
explain, but there is no evidence of purpose in their 
origination. Even the locomotion of the Myxomycetes 
and the Diatoms shows no definite purpose except when 
it is clearly set up in response to some external stimulus. 
Though there is no particular differentiation of an 
anatomical character in any of the sense-organs of a 
plant, there is nevertheless a differentiation of a physio- 
logical nature in the direction of sensitiveness which will 
