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Show 296 DARWINIAN A. they remain unaffected. A touch sh~ws that t~e glistening drops are glutinous a~d e~tremely tenam~us, as flies learn to their cost on ahghtrng, perhaps to s1p the temptinO' liquid, which acts first as a decoy and then like birdlime. A small fly is held so fast, and in its struggles comes in contact with so many of these glutinous globules, that it seldom escapes .. The result is much the same to the rnsect, whether captured in the trap of Dionrea or stuck fast to the limed bristles of Drosera. As there are various plants upon whose gland_ular hairs or glutino?s s~rfac~s small insects are habitually caught and pensh, 1t m1ght be pure coincidence that the mos~ effectual arrange~ent of the kind happens to occur 1n the nearest relatives of Dionrea. Roth, a keen German botanist of the eighteenth century, 'Yas the first to detect, or at least to record some evidence of intention in Drosera, and to comp~re its action with that of Dionrea, which, through Ellis's account, had shortly before been made known in Europe. He noticed the telling fact that not only the bristles which the unfortunate i.nsect had come in contact with, but also the ~urroundmg rows, before widely spreading, curved inward one ~y ?ne, · althouO'h they had not been touched, so as w1thm a few ho~rs to press their glutinous tips likewise against the body of the captive insect-thus doubling or quadrupling the bonds of the victim and (as w_e may now suspect) the surfaces through which some part of the animal substance may be imbibed. For Roth surmised that both these plants were, .in their way, predaceous. He even observed that the disk of the Drosera-leaf itself often became concave and enveloped ..,. INSECTIVOROUS PLANTS. 297 the prey. These facts, although mentioned now and then in some succeeding works, were generally forgotten, except that of the adhesion of small insects to the leaves of sundews, which must have been. observed in every generation. Up to and even within a few years past, if any reference was made to these asserted movements (as by such eminent physiologists as Meyen and Treviranus) it was to discredit them. Not because they are difficult to verify, but because, being naturally thought improbable, it was easier to deny or ignore them. So completely had the knowledge of almost a century ago died out in later years that, when the subject was taken up anew in our days by Mr. Darwin, he had, as we remember, to advertise for it, by sending a "note and query" to th~ magazines, asking where any account of the fly-catching of the leaves of sundew was recorded. ' When Mr. Darwin takes a matter of this sort in hand, he is not likely to leave it where he found it. He not only confirmed all Roth's observations as to the incurving of the bristles toward and upon an insect entangled on any part of the disk of the leaf, but also found that they responded similarly to a bit of muscle or other animal substance, while to any particles of inorganic matter they were nearly indifferent. To minute fragments of carbonate of ammonia, bowever, they were ·more responsive. As these remarkable results, attained (as we are able to attest) half a dozen years ago, remained unpublished (being portions of an investigation not yet completed), it would have been hardly proper to mention them, were it not that independent observers were beginning to bring out .- . •' |