130 STUDIES IN ELECTRO-PHYSIOLOGY: 



Dioncea are excited by contact to pour out on to the surface 

 of their leaves acid digestive secretions, which are the 

 result of changes in the activity of the gland-cells. 



" The conduction of the stimuli received is due in 

 .animals to the existence of differentiated nerves. The 

 way in which it is carried out in plants has been much 

 debated, but since the discovery of the continuity of the 

 protoplasm through the cell -walls there is little doubt 

 that we have here a similar mechanism. . . . 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 physiological nature in 

 the direction of sensitiveness, which will equal if not surpass 

 the powers of the sense-organs of an animal. The tendril 

 of Passiflora appreciates and responds to a pressure which 

 cannot be detected by even the human tongue ; the 

 seedlings of Phalaris readily obey the stimulus of an 

 amount of light which is hardly perceptible to the human 

 eye. Many plants readily detect and respond to the ultra- 

 violet rays of the spectrum, which are utterly invisible 

 to man." 



In his thirty-fourth lecture, General Considerations of 

 Irritability,* Sachs said : " Returning from these general 

 considerations to definite comparisons between the animal 

 and the plant, I would make special mention of that 

 exceedingly remarkable phenomenon in animal life, termed 

 by its great discoverer, Johannes Miiller, the specific 

 energies of the sensory nerves. As is well known, we 

 understand by this fact that for instance the optic nerve 

 responds to any given excitation whatever with the sensa- 

 tion of light : true, this sensation is as a rule called forth 

 by the vibrations of the luminiferous ether, but even 

 electric currents or mere concussion or diseased conditions 

 impel the optic nerve to the sensation of light. In the 



* The Physiology of Plants. 



