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Show 172 SEN rrlVENESS OJ!' 'l'IIE APEX CHAP. III. n.ncl a third very slightly from tho porpondicubr and from tho cauterised side. .!Escultts hippocastanwn: S ensitiveness of the apex of the Radicle.-Bit of glass an<l squares of card were affixed with shellac or gnm-wn.tor to tho tips of 12 ra<liclos of the horse-ch ·stunt; and when those objects fell off, they were refixed ; but not in a single instance was any curvature thus cans <l. rrh.cso ma. sive radicles, one of which was above 2 inches in length and · 3 inch in diameter at its ba. e, seemed in. cnsible to so slight a stimulus as any mall att<wh d object. N evcrthol s, when the ap x ncount rod an ob taclc in its dowmntnl course, the growing part became o uniformly and symmetrically ·urvcd, that its appear· ance indicated not mere mechanical ben<ling, but increased growth along the whole convex side, due to the irritation of the apex. That this is the correct view may be inferred from the effects of the mor powerful stimulus of caustic. The bending from tho C<tutcrisccl sid o ·cnrrc<l much slower than in the previously described species, nnd it will perhaps be worth while to give our trials in detail. Tbe seeds germinated in sn.wclust, n.nd one Ride of the tips of the radicles were slightly rubbed once with dry nitrate of silver; and after a few minutes were allowed to <lip into water. They were subjected to a rather varying temperature, generally between 52° and 58° F. A few cases lmvo not been thought worth recording, in which tho whole tip \Yas blackened, or in which the seedling soon became unhcaltl1y. . (1.) The radicle was slightly deflected from tho canten ·ed side in one day (i.e. 24 h.); in three clays it stood at 60~ from the perpendicular; in four days at 90° ; on the fi~th day 1t ~v:~ curved up about 40° above tho horizon; so that 1t had prrs through an angle of 130° in tho five clays, and this was the greatest amount of curvature ohserveu. d . (2.) In two days radicle slightly defle.cted; after seven a)S CHAP. III. OF TilE UADICLE OF JE,'OULUR. 173 deflected u9° from the perpcndicul:u and from the cauterised side; after eight days tho angle amounted to nearly U0°. (3.) After one day slight deflection, but tl1u cauterised mark was so faint that the same side was again tondwu with caustic. in four days from tho first tonch deflection amounted to 78°, which in an additional day increaseu to 90°. (4.) After two clays slight .dcfl ctiou, which during the next three days certainly increased but uevcr h came groat; the radicle did not grow well and died on tho eighth clay. (5.) After two days very slight doficction ; lrut this on the fourth day amounted to 56° from tho perpendicular and from the cauterised side. (6.) After three days doubtfully, but after four day, certainly deflected from tho cauterised side. On the fifth clay defl ction amounted to 45° from the perpcmlicular, and this ou the seventh day inorenscd to about 00°. (7.) After two days shghtly deflected ; on the third <lay the deflection amounted to 25° from tho perpendicular, anu this did not afterwards increase. (8.) After one day deflection uistinct; on tho thiru day it a~ounted to 44°, and on the fourth day to 72., from tho perpendiCular and the cauterised side. (9.) After two days deflection slight, yet distinct; on the third day the tip was again touched on tho same siuo with caustic and thus killed . . (10.) After ono day slight deflection, which after six days mm·eased to 50° from tho perpenuicnlal' and tho cauteri eel side. . (11.) After one day decided clcflcctiun, ·which after six dayR !~creased to 62° from tlw perpendicular anu from tho cauterised s1de. (12.) After one day slight deflection, w11ich on tho ccond day amounted to 35°, on tho fomth day to 5()0 , tmcl the ixth day to 63° from the perpendicular and the cn.uteri.-ed side. (1~.) Whole tip blackened, but more on one side than tl1e ~ther; on the fourth day slightly, and on the ixth day greatly ~fleeted from the more blackened side; tho deflection on tho nmth day amounted to 90° from the perpendicular. (14.) Whole tip blackened in tho same manner as in tho last ~ase; on the second day dcciucd deflection fl'Om tho more 9~~r.kened side, wl:ich incrca8cll on the seventh day to nearly • on the followmg day the ntdicle a1)pcarc<l unhealthy. (15.) Here wo had the anomalous case of a mdiclc bonding |