366 CONCLUDING REMARKS Chap. XV. 



ment, there is a great difference in the action of 

 allied fluids ; for instance, between certain vegetable 

 acids, and between citrate and phosphate of ammonia. 

 The specialised nature and perfection of the sensitive- 

 ness in these two plants is all the more astonishing 

 as no one supposes that they possess nerves ; and by 

 testing Drosera with several substances which act 

 powerfully on the nervous system of animals, it does 

 not appear that they include any diffused matter 

 analogous to nerve-tissue. 



Although the cells of Drosera and Dionsea are quite 

 as sensitive to certain stimulants as are the tissues 

 which surround the terminations of the nerves in 

 the higher animals, yet these plants are inferior even 

 to animals low down in the scale, in not being affected 

 except by stimulants in contact with their sensitive 

 parts. They would, however, probably be affected by 

 radiant heat ; for warm water excites energetic move- 

 ment. "When a gland of Drosera, or one of the fila- 

 ments of Dionsea, is excited, the motor impulse radiates 

 in all directions, and is not, as in the case of animals, 

 directed towards special points or organs. This holds 

 good even in the case of Drosera when some exciting 

 substance has been placed at two points on the disc, 

 and when the tentacles all round are inflected with 

 marvellous precision towards the two points. The 

 rate at which the motor impulse is transmitted, though 

 rapid in Dionsea, is much slower than in most or all 

 animals. This fact, as well as that of the motor 

 impulse not being specially directed to certain points, 

 are both no doubt due to the absence of nerves. Never- 

 theless we perhaps see the prefigurement of the forma- 

 tion of nerves in animals in the transmission of the 

 motor impulse being so much more rapid down the 

 confined space within the tentacles of Drosera than 



