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 anaesthetic 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 degree 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 



