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Show 36 DROSERA ROTUNDIFOLIA. CHAP. II. though the secretion is so viscid that it can be reInoved with difficulty merely by waving the leaves in water. If the falling drops of water are small, they adhere to the secretion, the weight of which must be j ncr eased in a In uch greater degree, as before reInarked, than by the addition of n1inute partic.les of solid matter; yet the drops never cause th tentacles to become inflected. It would obviously have been a oTeat evil to the plant (as in the case of occasional b . touches) if the tentacles were exc1ted to bend by every shower of rain; but this evil has b on avoiued by the glands either having b con1e through habit insensible to the blows and prol nged pr ssuro of drops of water, or to their having b en originally rendered sensitive solely to the contact of solid bodies. We shall hereafter see that th filaments on the loaves of Dionooa are likewise insensible to tho impa.ct of fluids, though exq uisi tel y sensitive to mo1non tary touches from any solid body. \Vhen the pedicel of a tentacle is cut off by a sharp pair of scissors quite close beneath the gland, the tentacle generally becomes inflected. I tri d this experiment repeatedly, as I was much surprised at the fact, for all other parts of the pedicels are insensiLle to any stimulus. These headless tentacles after a tin1e re-expand; but I shall return to this subj ct. On the other hand, I occasionally succe d d in crushing a gland between a pair of pincers, but this caused no inflection. In this latter case th t ntacles seem paral ysecl, as likewise follows from the action of too· strong solutions of certain salts, and by too great heat, whilst weaker solutions of the same salts and a more gentle heat cause movement. We shall also see 1n future chapters that vanous other fluids, some CHAP. II . . DROPS OF WATER. 37 vapours, and oxygen (after the pi t h b time excluded from its action) anll . als ee~ for SOine d h . . . ' a Inc uce 1nfi t' an t Is likewise results from . l eo Ion, current.* an lnc need galvanic• * My son Francis, guided b the observations of Dr. Burdo~ ~anderson on Dionroa, finds that If two needles are inserted into the blade of a leaf of Drosera th t~n~acles do not move; but that i~' t:>mnlar needles in connection with ~he secondary coil of a D B . , tmhd uctive apparatus ai·e insue rteOdis e tentacles curye inwards in th' course of a few minutes M e hopes soon t 1 r· . y son f h . b 0 ~u) Ish an acconnt 0 Is o servatwns. |
