OCR Text |
Show 126 COTYLEDONS SENSITIVE CrrAP. II. pin in this part, they rose up :ortically; but the blade was fo?nd also to be sensitive, care bavmg boon taken that tho pulvmus was not touched. Drops of water placed quietly on those cotyledons produced no effect, but an extremely fine stream of water, ejected from a syringe, ca~sed t~10m. to mo~e upwards. .When a pot of seecllings was rapidly hit. with a s~ICk and thus ~a1~re~, the cotyledons rose slightly. "\vhon a mmute lhop of mtnc acid was placed on both pulvini of a seedling, the cotyledons rose so quickly that they could easily be seen to move, and almost immediately afterwards they began to fall; but the pulvini had been killed and became br~wn. . The cotyledons of an unnamed spoc10s of Cassw (a largo tree from S. Brazil) rose 31° in the course of 26m. after tho pulvini and the blades bad both been rubbed dming J m. with a twig; but when the blade alone was similarly ruhl,od tho cotyledons rose only 8°. The remarkably long and narrow cotyloU.ons, of a third unnamed species from S. Brazil, did not move when their blades were rubbed on six occasions with a po:inted stick for 30 s. or for 1m.; but when the pulvinus was rubbed and slightly pricked with a pin, tho cotyledons rose in the conrs0 of a few minutes through an angle of 60°. Several cotyledons of C. neglectu (likewise from S. Brazil) rose in from 5 m. to 15m: to various angles between 16° aml 34°, after being rubbed durmg 1m. with a twig. Their sensitiveness is retained to a f:omcwhat advanced age, for the cotyledons of a little plant of G. ,. e.r;lccta, 34 days old and bearing throe true loaves, rose when lightly pinched between the finger and thumb. Some seecllings were exposed for 30m. to a wind (temp. 50° F.) sufficient!~ str?ng to keep the cotyledons vibrating, but tbis to our surpr.Iso d1~ not cause any movement. The cotyledons of four scecllmgs o[ the Indian C. gluucawere either rubbed with a thin twig for 2m .. or were lightly pinched: one rose 34° ; a second only 6° ;. a :hml 13° · and a fourth 17°. A cotyledon of 0 . jloridu SID1Jhuly tre;ted rose 9°; one of G. corymbosa rose no, and one of tl~e very distinct G. mhnosoides only 6°. Those of C. z;ubeoceus di~ not appear to be in the least sensitive; nor were those of C. t/(,dosa, but these latter are rather thick and fleshy, and do not rise at night or go to sleep. . . . f Smithia sensitiva.-This plant belongs to a clistmct sub-01de~o the Leguminosre from Cassia. Both coty lodons of an oldish seedling, with the first true leaf partially unfolded, were rubbed for l m. with a fine hrig, and in 5 m. each rose 3~0 ; they CHAP. II. TO CONTACT. 127 remained in this position for 15m., but when lookotl at again 40m. after the rubbing, each had fallon 14°. Both cotylc<lons of another and younger see<lling were lightly rubbed in tho same manner for 1m., and after an interval of 32m. each had riseu 30°. They were hardly at all sensitive to a fino jet of water. The cotyledons of S. Pjund'ii, an African water plant, are thick and fleshy; they are not sensitive and do not go to sleep. Mimosa pudica and albidct.-Tho bla.dos of several cotyledons of both these plants were rubbed or slightly scratched with a needle during 1m. or 2m.; but they did not move in the least. When, however, tho pulvini of six coty lodons of M. pudica were thus scratched, two of them were slightly raised. In these two cases perhaps the pulvinus was accidentally pricked for on pricking the pulvinus of anothm· cotyledon it rose a little. It thus appears that the cotyledons of lVIimosa are loss sensitive than those of the previously mentioned fJlants.* Ox~lis sens~tiurt.-The blades and pulvini of two cotyledons, st~ndmg bonzontally, were rubbed or rather tickled for 30 s. With a fine split bristle, and in 10m. each had risen 48° · ~hen looked at again in 35m. after being rubbed they hacl l'lSen 4° more;. a~ter 30 additional minutes they were again horizontal. On h1ttmg a pot rapidly with a stick for 1m., the cotyledons of two seedlings were considerably raised in tho course ?f 11m. A pot was carried a little distance on a tray and thus Jolted; and the cotyledons of four seedlings wore all raised in lOom.; after 17m. one had risen 56°, a second 45°, a third almost 90, and a fourth 90°. After an additional interval of 40 m. three of t?em had re-expanded to a considerable extent. These observat~ ons were made before we wore aware at what an extraordin. anly rapid rate tho cotyledons circumnutate, and arc therefore ~lable to en:or. N~vertholess it is extremely improbable that tho otyled~ns m tho CJght cases given, should all have been rising ~ th~ ~1me when they wore irritated. Tho cotyledons of UJ al'is al~t~lana and r·osea were rubbed and did not exhibit any sensitiveness. Finally, there seems to exist some relation between 1 ,"f The sole notice which we lave met with on tile sonsitivene~ a of ~otyledons, relates to Mimosa; lor Aul!. P. De Canuolle says (' Pbys. V eg.,' 1832, tom. ii. p. 865), "lcs cotyledons du M. pudica tenuent a so raprochcr par leurs faces tmpel'icure:; lorsqu'on los irrito. ·• |