* ‘Arbeiten Bot.  Inst.  Würzburg,’ Heft iii. 1873, p. 398.

[page 132] hereafter see, Sachs discovered that the radicle a little above the apex is sensitive, and bends like a tendril towards the touching object.  But when one side of the apex is pressed by any object, the growing part bends away from the object; and this seems a beautiful adaptation for avoiding obstacles in the soil, and, as we shall see, for following the lines of least resistance.  Many organs, when touched, bend in one fixed direction, such as the stamens of Berberis, the lobes of Dionaea, etc.; and many organs, such as tendrils, whether modified leaves or flower-peduncles, and some few stems, bend towards a touching object; but no case, we believe, is known of an organ bending away from a touching object.

Sensitiveness of the Apex of the Radicle of Vicia faba.—­Common beans, after being soaked in water for 24 h., were pinned with the hilum downwards (in the manner followed by Sachs), inside the cork lids of glass-vessels, which were half filled with water; the sides and the cork were well moistened, and light was excluded.  As soon as the beans had protruded radicles, some to a length of less than a tenth of an inch, and others to a length of several tenths, little squares or oblongs of card were affixed to the short sloping sides of their conical tips.  The squares therefore adhered obliquely with reference to the longitudinal axis of the radicle; and this is a very necessary precaution, for if the bits of card accidentally became displaced, or were drawn by the viscid matter employed so as to adhere parallel to the side of the radicle, although only a little way above the conical apex, the radicle did not bend in the peculiar manner which we are here considering.  Squares of about the 1/20th of an inch (i.e. about 1 ½ mm.), or oblong bits of nearly the same size, were found to [page 133] be the most convenient and effective.  We employed at first ordinary thin card, such as visiting cards, or bits of very thin glass, and various other objects; but afterwards sand-paper was chiefly employed, for it was almost as stiff as thin card, and the roughened surface favoured its adhesion.  At first we generally used very thick gum-water; and this of course, under the circumstances, never dried in the least; on the contrary, it sometimes seemed to absorb vapour, so that the bits of card became separated by a layer of fluid from the tip.  When there was no such absorption and the card was not displaced, it acted well and caused the radicle to bend to the opposite side.  I should state that thick gum-water by itself induces no action.  In most cases the bits of card were touched with an extremely small quantity of a solution of shellac in spirits of wine, which had been left to evaporate until it was thick; it then set hard in a few seconds, and fixed the bits of card well.  When small drops of the shellac were placed on the tips without any card, they set