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(Brassica O.)

We shall here show that the upper part of the hypocotyl of seedlings cabbages when illuminated transmit an effect to the lower part , causing it to bend towards the light.

It is always necessary to experiment  on young seedlings about ½  inch in height or even a little less ; for when they have grown to 1 inch & upwards , the basal part under any circumstances ceases to bend . One experimenter We first tried painting the upper part of hypocoty with indian ink or cutting off the summits of the for various lengths, but these experiments are not worth giving, though they confirm as far they go, the following one which There was made, by folding by Bending once round the upper half of young hypocoty & painting it thickly with Indian ink, — As a contrast were first 12 hypocoty were had an upper portion wrapped in the skin, which we left unpainted & these all became greatly well or greatly curved generally as excepting one &

this was only moderately well curved towards the light [relocation indicated from before 'excepting' above) Twenty other young hypocotys had the gold-beters sking round there upper half painted with indian ink, while there lower part was left open to unprotected the light, & they were exposed in a box open in front & blackened within & open on all the other side)  before 'or' below for 7' for 7 to 8 before a S. W window (bay or before a high paraffin lamp); & this time was amply sufficient to as shown by the heliotropism of the summits; cause all for to for seedling in the same Pots to become greatly bowed ; but some were first exposed for a much longer time. — Of these 20 hypocoty thus treated 14 remained quit vertical; & 6 became slightly inclined bowed to the light ; but 2 of other were not really exception , for on removing the g. br. skin, it the p[illeg] it was found penetrate by numerous small 43 transparent spines on the side facing the light . The par In 2 other cases ,moreover, the panted skin did not extend 1/2 way down the hypocotyl ; Altogether there was a

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The other 13 cotyledons w became bowed to in the direction of obliquely toward the window ; one pointed at an angle of only 18° from the window it , but the other 12 twelve at angles varying between 45° & 60°. from the window .—    At the commencement of the experiment pins were laid on the earth in the pots , in the direction towards which the cleared stripe on them faced pointed & in which direction the diffused light struck could enter; & in 7 of these 13 cases the cotyledon pointed directly towards in the lines of the pins & in 6 cases in a line between that of the pin & that of the window. This intermediate direction is intelligible for any light proceeding obliquely from the sky through the cleared stripe slits w be much more deficient efficacy than the diffused light not entering directly through it. The contract in appearance after the 8 exposure between these 13 cotyledons, & all the ones other many other seedlings a in the same pots, which were all (excepting the [illeg words] in parallel lines together & all (excepting the above 14 active ones) with greatly bowed in straight & parallel lines directly towards the window, were very extremely striking . It is therefore obvious certain. that a very little & weaker weak light, which striking the upper half of the cotyledon of Phalaris us far more potent in determining the direction of the curvature of the lower part, than the full illumination of this latter part during the whole time of exposure.)

 

(In confirmation of this result it may is may be with noticing that the summits of 3 Cots were painted laterally on one side with thick indian ink to a depth of .2 inch from the spires; ; & the whole lower part being left fully opened ;, & these 3 became deflected towards the unpainted sides of the tip summits , at angles of 31°, 35° & 53° from the direction of the window.)

[sketch]

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(Even if we assume that the greater illumination of one side of any part of a plant inevitably tends to cause the plant a it to bend to this side— though such an assumption if fully contradicted by the former experiments on seedlings — even in this case the tendency differs greatly in different species — & in smaller in degree individuals of the same specs, as may be seen in almost ay any parts of the cotys of a [illeg] plant*[illeg] & Therefore so that [illeg words] it may readily be modified to any extent or degree if the modification can be the groundwork for its of the effect tendency to any extent or deg degree beneficial to the plant. Thus When a plant [illeg] lives chiefly by catching insects & does not benefit by its having the leaves beings turned towards the light, they cease to be heliotropic as we see the power of movement is lost, as with Drosera. The plants with strong stems were drawn toward the light, they w often leave there supports & [illeg words]

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with the structures, by which the certain seeds of certain Genera bury themselves in the ground * — are the direct result of follow from the required drying of one side of the organ parts in question ; yet no one will suppose that all this has been effected without special adaptation.

Similarly we are led to believe in adaptation when we see the hypocotys of one seedling seedlings which is are green contain chlorophyll & can disperse carbonic acid, bending to the light ; so that for it this the receives but little light & are is shaded by the cots, which are however [illeg words] become fully exposed to the light & the hypocoty therefore may be said thus to sacrifice themselves itself for the good of the cotyledons. But if the organ is be prevented from bending, as must often sometimes occur when seedlings spring up in [illeg words]

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Finally the cotyledon & leaves of plant may be strongly heliotropic, to their great advantage when growing in a totally shaded side, & yet as we attempted to show in a former chapter they are be able to resist remain all day horizontal & fully exposed to the lightly by resisting the tendency to bend upwards which must be caused —  can hardly fail to [illeg] follow from follow from by from the very difference in degree of illumination of the upper & lower surfaces. . But as the tension apparently goes on increasing all day when with the increasing length of the evening & as soon as it will that way list is not disadvantage for the plant to yield, the circumnutating leaves rise can a little as we know in the evening & this occurs in my case is of frequently occurs.

This resistance to an upward movement, as long as the light comes from above, is [illeg] very different what D Frank has called designated by the term transverse-heliotropism. The horizontal position of leaves during the day, & which we attribute to their resisting for a time a tendency always present to bend upwards.

they are found to yield [illeg] last & rise as [illeg] in the evening