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Show 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 a1nmonia. The specialised nature and perfection of the sensitiveness in these two plants is all the more astonishing as no one supposes that they possess nerves; and by testino· Drosera with several substances which act 0 f . powerfully on the nervous systen1 o an1mals, it does not appear that they include any diffused n1atter analogous to nerve.-tissue. Although the cells of Drosera and Dionma are quite as sensitive to certain stimulants as are the tissues which surround the tenninations of the nerves in the higher animals, yet these plants are inferior oven to anim.als 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 xcites energetic n1oven1ent. When a gland of Drosera, or one of tho :filaments of Dionma, is excit d, the motor in1pulso radiates in all directions, and is not, as in the case of animals, directed towards special points or organs. 1'his 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. 'rhe rate at which the motor impulse is transrnitted, though rapid in Dionroa, is much slow r than in most or all animals. This fact, · as well as that of the motor impulse not being specially directed to certain poin~s, are both no doubt due to the absence of nerves. Nevertheless we perhaps see the prefigurement of the formation 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 CHAP. xv. ON THE R E .. .\. E£. elsewhere, and somewhat m r rapid in n 1 n~itn linn 1 than in a transv r lir ti n ~ ·r th di"' ·. 'I h '~ plants exhibit still 111 r. rlninly th ir inf ri< rity to animals in the ab n f ( n ,. r tl so far as the glan l f distance, send ba k contents of the c ll t bases of the ten ta 1 "'. all is the absence f a impressions from all p int to tran 1nit th ir in any definite clir ti n to t r th m ur c. n l r 1 r - duce them |