| OCR Text |
Show 144 SENSITIVENESS OF TilE APEX CHAP. Ill,' ts of very thin o·lass, &c., were affixed at different men b · f 55 d' l t . to one side of the conical t1ps o ra 1c es. liDOS h 1 .. The 11last-mentioned cases, but not t o pre 1mmary ones, are here inclucled. The squares. , &c., were most 19 . h commonly affixed with shellac, but In cases Wit thick gum-water. vVhcn the latter ';as usocl, the squares were sometimes found, as previOusly stat:u, to be separated from tho apex Ly a layer of thiCk :fluid, so that there was no c.ontact, and conse· quent ly no bondin(b) ' of the racl10le ; ancl. such fe.w cases were not recorded. But in every Instance m which shellac was employed, unless the square fell off very soon, the result was recorclcc~. In several instances when the squares became displaced, so as to stand parallel to the radicle, or were separated by fluid from the apex, or soon fell off, fresh squares were attach eel, and these eases ( doscriLed under the numbered paragraphs) are here included. Out of 55 radicles experimented on under the propo~ tempe· rature, 52 became bent, generally t a constdcrable extent from the perpendicular, ancl away from the side to which the object was attached. Of the t~ree failures, one can be accounted for, as the radicle became sickly on the following day; and. a second was observed only during 11 h. 30m. As m several cases the terminal growing part of the racliele con.tinuo? for some time to bend from the attaehecl obJeCt, 1t formed itself into a hook, with the apex pointing to the zenith, or even into a ring, ancl occasionally into a spire or helix. It is remarkable that those latter cases occurred more frequently when objects were attached ,vith thick gum-water, which never became dry, than when shellac was employed. Tho curvature was often well-markecl in from 7 h. to 11 h.; and in one instance a semicircle was formed in 6 h. 10m. from the time CHAP. III. OF THE RADICLE OF THE BEAN. 145 of attachment. But in order to see the phenomenon as well displayed as in the above described cases, it is indispensable that the bits of card, &c., should bP made to adhere closely to one side of the conical apex; that healthy radicles should be selected and kept at not too high or too low a temperature, and apparently that the trials shuulcl not be made in the middle of the winter. In ten instances, raclicles which ha<l curved away from a square of card or other object attached to their tips, straightened themselves to a certain extent, or even completely, in the course of from one to two dayR from the time of attachment. This was more especially apt to occur wh n the curvature was sliaht. But in one instance (No. 27) a radicle which in 9 h. had been deflected about 90° from the }Jorpendicular, became quite straight in 24 h. from the period of attachment. With No. 26, the radicle was almost straight in 48 h. vVe at first attributed the strai()'htening process to the radicles becoming accustomed to a slight stimulus, in the same manner as a tendril or sensitive petiole becomes accustomed to a very light loop .of t~read, and unbends itself though the loop remams still suspended; but Sachs states* that radicle~ of t~e bean placed horizontally in damp air aft"r curvmg downwards through geotropism, straighten themselves a little by growth aloncr their lower or 'd b concave SI es. Why this should occur is not clear· but perhaps it likewise occurred in the above te1; cases. There is another occasional movement which must not be passed over: the tip of the radicle, for a length of from 2 to 3 mm., was found in six instances, • 'Arbeiten Bot. Instit., Wiirzburg,' Heft iii. p. 456. L |
