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Show 32 DROSER A ROTUNDIFOLIA. . . l d and caused this rapJd into contact with t~e f a~ s,dued to some distilled CHAP. II. Inovement. Accordin~ty . n~cent substance, namely, . h of a qui e In . f water a pinc f 1. which consists o an P . . d ·bonate o Ime, . _, h t recipitate car h k th mixtur ' anu t us go l der . I s oo . d . iinpalpab e po~ .' k T leaves were Imm rse In a fluid like thin mil . wo ·y tentacle was much . 6 almost ever h it and 1n m. f th se 1 aves under t e ' I 1 ced one o . d inf.l ected. Pd a saw I. nnumer· able atoms o. f hmSe a - mic.r oscopet,h an xterna1 sur· fa c e of the secretion. h orne, henng to e e d . t d wer lying on t e sur-however, had penetrated l ' dan bt it was th se particles f h 1 ds . an no ou . . faces o t e g an ' b d When a 1 af IS Im-d th t ntacles to en · which ca.u se t e. teh e secre t1' on l·nstantly swells much; mersed In wa er' . . ptured here and there, so that 1t IS ru d and I presume h . If so we can un or-del. f ater rus In. ' that little e Ies o w f h lk which r sted on t.he h th a toms o c a ' · stand ow e d h d enetratecl the secretwn. surfaces of the glan s, da . p . . tated chalk between h has rubbe precipl . Anyone w o . . eivod h w exo sslv ly fine his fingers _wlll ha~e E~r~here must be a limit, beyond the powder 1~. No ~~ b too small to act on a gland ; which a particle w?u. ek t I hav often seen h. r l t lS I now no . but what t lS llll h" h had fall n from the air, on the fibres and dust, w lC . ailcl these never 1 t k pt In my roonl, glands of p an s e . b t th n such particles lay 1. n d ucecl any movement ' ut ' . cl n ver r ac h ecl th e on the surface of the secre Ion an gland itself. a· . fact that a little F . 11 it is an extraor Inary c • ·h- Ina y, . h in length ancl weig bit of soft thread, -l-o of an Inc h . , s_ _ of an • 1 f a grain or of a human au, TOo o . 1ng sT-!T""f 0 ' . . 1 __t_ of a gram inch in lengt~ and welghmg ~~ y '' 'i o reci ita ted (·000822 milhgramme ), or particle~ o p pg·land, chalk, after restm· g fo r a .s ho"rt t tinU1 s eoxnc itian g them should indue~ some change In l s ce ' CHAP. II. INFLECTION DIRECTLY CAUSED. 33 to transmit a motor impulse throughout the whole length of the pedicel, consisting of about twenty cells, to near its base, causing this part to bend, and th(~ tentacle to sweep through an angle of above 180°. That the contents of the cells of the glands, and afterwards_ those of the pedicels, are affected in a plainly visible manner by the pressure of minute particles, we shall have abundant evidence when we treat of the aggregation of protoplasm. But the case is 1nuch more remarkable than as yet stated; for the particles are supported by the viscid and dense secretion ; nevertheless, even smaller ones than those of which the measurements have been given, when brought by an insensibly slow movement, through the means above speci:fied, into contact with the surface of a gland, act on it, and the tentacle bends. The pressure exerted by the particle of hair, weighing only 78-}40 of a grain and supported by a dense fluid, must have been inconceivably slight. We may conjecture that it could hardly have equalled the millionth of a grain; and "\-ve shall hereafter see that far less than the millionth of a grain of phos ·phate of ammonia in solution, when absorbed by a gland, acts on it and induces movement. A bit of hair, -~ of an inch in length, and therefore 1nuch larger than those used in the above experiments, was not perceived when pla~ed on my tongue ; and it is extremely doubtful whether any nerve in the human body, even if in an infla1ned condition, would be iu any way affected by such a particle supported in a dense fluid, and slowly brought into contact with thA nerve. Yet the cells of the glands of Drosera are thns excited to transmit a motor impulse to a distant point, inducing movement. It appears to me that hardly any more remarkable fact than this has been observed in the vegetable kingdom. D |
