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Show 4.G8 'fRANSMIT'rED EFFECTS OF LIG ll'r . CuAr. IX. with a mixture of oil and lamp-black, and wore then exposefl before a window; others similarly treated were afterwards tried in darkness. 'rhcso cotyledons soon became plainly bowed towards the blackened side, evidently owing to the grease on this side having ehcckod their growth, whilst growth continued on the opposite side. But it deserves notice that tho curva· ture difC rod from that causml by lio·ht, which ulti· mately becomes abrupt ncar the ground. These seedlings did not afterwards die, but were much injured and grew badly. LOCALISED SENSITIVENESS TO LIGHT, AND IT. TRANSMITTED EFFECTS. Phalaris Oana?~iensis.-Whilst observing the accu· racy with which the cotyledons of this plant became bent towards the light of a small lamp, we were impressed with the idea that the uppermost p<trt deter· mined the direction of the curvature of tho lower part. \Vhen the cotyledons are exposed to a btoral l1~ht, the upper part bends first, and afterwards tho bcndmg gradually extends down to the ba,so, anu, as we shall presently see, even a little bonoat~1 the ground. This holds good with cotyledons irom less t~an ·1 inch (one was observed to act m· tl n·s mam 1e.r wh1c.b was only ·03 in height) to about ·5 of an mc~t 1; 1 height· but when they have gro·wn to nearly an mcf1 in heig'· ht the basal 1mrt, for a length of ·lr;;Jt o.rJ"'.o I. au inch a' bove the ()'round, ceases to 1u. en d· Aswd' rtu l d 0 )roung· coty e · ons t }1 e 1o wer pa.r· t bo ·oes on ben wg!~· after the upper part has become we ll ar.c b ed tow. al'CN lt. t ly I)omt to ·t lateral light the al)ex would u 1ma e t< he ground ins't ead of to the h•g ht, d.1 ·d no t t.h e ulfp paesr part reverse its curvature and straighten Itse ' CuAP. IX. TRANSMITTED EFFECTS OF LIGHT. 469 soon as the upper convex surface of the boweddown portion received more light than the lower concave surface. The position ultimately assumed by young and upright cotyle lons, expose~ to lig~t entering obliquely fro~ above throu~h a wmdow, 1s show.n in the accompanymg figure (Fig. 181); and here It may be seen that the whole upper part has become very nearly straight. When the cotyledons were exposed before a bright lamp, standi~g on the same level with them, the upper part, whiCh was at first Fig. 181. Pilnlaris Oanariensis: coty leclons after exposure in a box open on one side in front of a south-west window during S h. Curvature t owards th e. light accurately traced. The short horizontal lines show the level ot the ground. greatly arched towards the light, became straight and strictly parallel with the surf<:tce of the soil in the pots; the basal part being now rectangularly bent. All this great amount of curvature, together with the subsequent straightening of the upper part, was often effected in a few hours. After the uppermost part has become bowed a little to the light, its overhanging weight must tend to increase the curvature of the lower part; but any such ofi'ect was shown in several ways to be quite insignificant. When little caps of tin-foil (hereafter to be described) were placed on the summits of the cotyledons, though this must have added considerably to their weight, the rate or amount of bonding was not thus increased. But the best evidence was afforded by placing pots with seedlings ofPhalaris before a lamp in such a position, that the cotyledons were horizontally extended n.nd projected at right angles to the line of light. In the course of fi1 h. they were directed towards the light with their bases bent at right n.ngles; and this n.brupt |