158 WHAT IS A PLANT? 



was based on this supposition, plants being devoid of any such 

 power. Sensation was, moreover, thought to be invariably 

 accompanied by the presence of a nervous system. What 

 do we find to be the case ? We now look on a " nerve " as 

 simply " a linear tract of specially modified protoplasm between 

 two points of an organism — one of which is able to affect the 

 other by means of the communication so established."'" One 

 of the chief properties of profoplasvi^ the living substance of 

 plants and animals, is '''' contractility '^ All contraction ensues as 

 the result of the application of some " stiniulns^''' such as light, 

 heat, electricity, mechanical irritation, and the like, or by the 

 exercise of the will. The phenomenon of " reflex action " in 

 animals is familiar to all. Stating it simply, in the case of any 

 external stimulus, the " impulse " is sent along a " sensory " tract 

 of nervous matter to the brain, and thence reflected along a 

 '' motor " pathway to the muscles, causing movement or contrac- 

 tion in them. Touch one of the tentacles of a snail, and it is 

 instantly retracted. This is due to irritation of the nervous sys- 

 tem acting on the muscles, and causing them to contract. In the 

 anemone, although no definite nervous system is present, yet, 

 taking the above definition of a nerve, we can understand the 

 evidence the creature gives of sensation by the immediate with- 

 drawal of its circlet of tentacles. We can easily demonstrate 

 reflex action in ourselves by placing our fingers in boiling 

 water, or by touching a hot cinder. We execute a similar hasty 

 retreat. 



Now, protoplasm in animal and plant is absolutely identical. 

 The contractility in that of a plant can in no way be distinguished 

 from the contractility in that of an animal. Furthermore, Dr. 

 Burdon-Sanderson, in 1873, ^'^ Darwin's suggestion, undertook 

 some experiments on contractility, as seen in the protoplasm of 

 our old friend, DiojKsa. He found this to be accompanied by an 

 ^^ electrical distti?imnce,'^ precisely similar to that taking place when 

 a human muscle, such as the " biceps," contracts, as in bending 

 the arm. Among plants, we find numerous cases of protoplasmic 

 contractility ensuing as a result of stimuli of various kinds, analo- 

 gous to that taking place by the agency of nervous tissue. We 

 ^^ iiu.\ley, '' Science and Culture," p. 158. 



