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Show 34 DROSERA ROTUNDIFOLIA. CHAP. II. . the Exterior Tentacles, when their Glands The Injlect~on of 't d by Re'Y1eated Touches. are exc~ e r that if the central glands We have already .seen tly' brushed they trans- . d b being gen ' are. excite tor Y.I mpu1 s e t o the exterior tentacles, rnit a mo b d. and we have now to con- cau. stihenm gto he.n h' '£ llow from the g1 a nu,, s of ' . ·a th effects w Ic o h d 0 si er e. 1 bein . themselves touc . n the extenor t~ntac es lar ! number of glands were several occasions, a . g dle or fine brush, 1 e with a nee touched on y oncb d th whol flexibl tentacle; d h to en e d har enoug . t have caused a thousan - and though this mutsh (,the weig·ht of the above ld t pressure an 0 fo grea er . t tentacle mov d. n described pa~ticles, n~ a lands on eleven loaves another occasion forty- . ve g thrice with a h d nee twice or even ' were touc e. o . 'le This was done as quickly as needle or stiff bnst . ffi . t t b nd the ten- . b t 'th force su cien o possible, u WI · fl t d - three . t onl six of them became In ec ' tacles , ye Y . a sli h t degree. In order to plainlty~ and h:~~:: ~~ese fentacles which were not ascer ain w . ffi . t tate bits of meat were ffi t d re In an e cien s ' 1 a ec e we f th m and they all soon b came great y placed on ten o e ' d hen a large number of in curved. On the other han ' w . . .. th the glands were struck l~O Ur, :fi ve, or six ht im. es WliIn ter of same force a.s b e1~o r.e , a needle or s a· r P sfp' t tacle~ h 1 . proportion o en " glass being used, a muc harger lt was so uncertain became I· n fl ec t ed .' but t e res.u t I struck I.n as to seem capricious. For Ins a~ce, ha ened to the above manner three glands, which . p~ fleeted be extremely sensitiv_e, a_nd all thr ~a;~:e~n placed almost a.s quickly as If bits ~f meat c • ale for· on them. On another occasion I gave a sinb CHAP. II. THE EFFECTS OF REPEATED TOUCHES. 35 cible touch to a considerable number of glands, and not one moved ; hut these same glands, after an interval of some hours, being touched four or :five time~ with a needle, several of the tentacles soon became inflected. The fact of a single touch or even of two or three touches not causing inflection must be of some service to the plant; as during stormy weather, the glands cannot fail to he occasionally touched by the tall blades of grass, or by other plants growing near ; and it would be a great evil if the tentacles were thus brought into action, for the act of re-expansion takes a considerable time, and until the tentacles are reexpanded they cannot catch prey. On · the other hand, extreme sensitiveness to slight pressure is of the highest service to the plant; for, as we have seen, if the delicate feet of a minute struggling insect press ever so 'lightly on the surfaces of two or three glands, the tentacles bearing these glands soon curl inwards and carry the insect with them to the centre, causing, after a time, all the circumferential tentacles to embrace it. Nevertheless, the movements of the plant are not perfectly adapted to its requirements; for if a bit of dry moss, peat, or other .rubbish, is blown on to the disc, as often happens, the tentacles clasp it in a useless manner. They soon, however, discover their mistake and release such innutritions objects. It is also a remarkable fact, that drops of water falling from a height, whether under the form of natural or artificial rain, do not cause the tentacles to move; yet the drops must strike the glands with considerable force, more especially after the secretion has been all washed away by heavy rain; and this often occurs, D 2 |