366 CONCLUDING REMARKS Onar. 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 Dionza 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 Dionza, 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 Diona, 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 
