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Show 242 ClRCUMNUTATION OF LEAVES. CrrAP. IV. seem to be continually opening and shutting to a very small extent. A nearly full-grown leaf (afterwards proved to be highly sensitive to contact) stood almost horizontally, so that by driving a long thin pin through the foliaceous petiole close to the blade, it was rendered motionless. The plant, with a little triangle of paper attached to one of the marginal spikes, was placed under a microscope with an eye-piece micrometer, each division of which equalled o-h of an inch. The apex of the paper-triangle was now seen to be in constant slight movement; for in 4 h. it crossed nine divisions, or 500 of an inch, and after ten additional hours it moved back and had crossed -a--Bo in an opposite direction. 'fhe plant was kept in rather too cool a place, and on the following clay it moved rather less, namely, 5h in 3 h., and o-to in an opposite direction during the next 6 h. The two lobes, therefore, seem to be constantly closing or opening, though to a very small distance; for we must remember that the little triangle of paper affixed to the marginal spike increased its length, and thus exaggerated somewhat the movement. Similar observations, with tho important difference that the petiole was left free and the plant kept under a high temperature, were made on a leaf, which was healthy, but so old that it did not close when its sensitive hairs were repeatedly touched, though judging from other cases it would have slowly closed if it had been stimulatctl by animal matter. The apex of the triangle was in almost, though not quite, constant movement, sometimes in one direction and sometimes in an opposite one; and it thrice crossed fi. ve eli visions of the micrometer (i.e. Ito of an inch) in 30m. This movement on so small a scale is hardly comparable with orclinary circumnutation; but it may perhaps be compared with the zigzag lines and little loops, by which the larger ellipses made by other plants are often interrupted. In the first chapter of thi. volume, tho rem:1rkable oscillatory movements of the circumnutatiug hypocotyl of the cabbage hn.ve beun described. The leave· of Dionroa present the same phenomenon, which is a wonderful one, as viewed under a low po,ver (2-inch object-gla. s ), with an eye-piece micrometer. of which each division (oh of an inch) appeared as a rather w~de space. The young unexpand.oclleaf, of which the circuronuta~lllg movements were traced. (Fig. lOG), had a glass fllament fixed porr)ond.icularlv• to it·' aml tho movement of the apex jw'\ats ohiierved in tho hot-house (temp. c\4° to ~6° F.), with 1 g 1 admitted only from above, and. with any lateral currents of all CIIAP. IV. DICOTYLEDONS. 243 excluded. The apex sometimes crossed on ... the micrometer at an imperceptibl slow -~or two d.Iv1s1ons of move. d to nwards by rapid starts 0r, J.Yer k s of m_~_o , but generally it 2 or a 1 . one ms ance of rooo of an inch. Aft . 1o?O. Hioo' anc m apex drew itself backwards with er .ea?h JOik forwards, the of the distance which had just ~ompar~tive slowness for part very short time made another· J. 0~kn ~gamed; and then after a · or 10rwards F . cuous Jerks forwards, with slower rotr . . our conspl-occasion to occm· in exactly one . cats, w_cre seen on one oscilla~ions. As far as we couldm~:uto, bcsiclos som~ minor ret.r eatmg lines did not CO.l llCI. de anJ dd ?If~ 'S Ot he ta dvancmg and el~pses were ea.ch time described ' S . ' ex remely minute qmte motionless for a short :. d omobmes tho apex remained the several hours of obs. e rvat IpOenn wo as· m. I tts' general c. ours.e durinc" n so that the leaf was probabl . ;o opposite dHection~o; A < Y mrcumnutatm()' ' n older leaf with the lobes full o· . afterwards proved to be hi hl Y _o~rmnded, and which was observed in a similarmannerg e:c se~~~Ive to contact, was next to a lower temperature in a r~om ep r, at tho pl~nt was exposed and backwards in tho 8 • I he apex oscillated forwards arne manner as b f • ward were loss in extent . b < c ore; but the jerks for- I . , VIZ. a out -L._ i h. 1 onger motiOnless periods A . 1ooo nc 'anc there were movements might be d . t s It appeared possiLle that the he l d close to the leaf d u.e o cunonts 0 f m·r , a wax taper wa" · urm()' one of th t· ,, no oscillations were th o d 0 mo wnloss periods but OS.C illa.tw ns commencedu s cauhs e · A.f to r 10 m., however, vigo' rous warmed and thus stimui~~~ ap~ owmg to tho plant having been bef~re long the oscillations c. h~ candle was then removed and ~gam after an interval of ~~.e~O ncv~rthelcss, ·~hen looked at the ~lant was taken back i t ~-, It was agam oscillating. ~llowmg morning was seen n o t w. hot~hou ·e, and on the VIgorously. Another old b to be osci llatm~, though not very least sensitive to a t hut hoal~hy leaf, which was not in the ~ays in the hot-houseouc ' was ·hkcwise ob orvccl clming two littl~jerks forwards or'a~~~t ~~tt~checl filament made many ~mally, to ascertain whe 1ooo or only l_ooo of an inch. petiOle oscillated th . thor tho lobes mclependent1y of th to the blade with sh:Ifotwle of an old leaf was cemented c1os: !he soil. But before tah~ to thedtop of a little stick driven into tOund t b IS was ono the 1 f been o e vigorously oscillating . . ·k~a was observed, and cemented to tho t· k OI .JCI mg; and after it had an inch still conti·n d s lC ' the oscillations of about -L- t' uo On the f' ll . 1ooo o · 0 owmg day a little infusion R 2 |