Sensitiveness of the tips of the Secondary Radicles of the Bean to contact.—­All the previous observations relate to the main or primary radicle.  Some beans suspended to cork-lids, with their radicles dipping into water, had developed secondary or lateral radicles, which were afterwards kept in very damp air, at the proper low temperature for full sensitiveness.  They projected, as usual, almost horizontally, with only a slight downward curvature, and retained this position during several days.  Sachs has shown* that these secondary roots are acted on in a peculiar manner by geotropism, so that if displaced they reassume their former sub-horizontal position, and do not bend vertically downwards like the primary radicle.  Minute squares of the stiff sanded paper were affixed by means of shellac (but in some instances with thick gum-water) to the tips of 39 secondary radicles of different ages, generally the uppermost ones.  Most of the squares were fixed to the lower sides of the apex, so that if they acted the radicle would bend upwards; but some were fixed laterally, and a few on the upper side.  Owing to the extreme tenuity of these radicles, it was very difficult to attach the square to the actual apex.  Whether owing to this or some other circumstance, only nine of the squares induced any * ‘Arbeiten Bot.  Inst., Würzburg,’ Heft iv. 1874, p. 605-617. [page 155]

curvature.  The curvature amounted in some cases to about 45o above the horizon, in others to 90o, and then the tip pointed to the zenith.  In one instance a distinct upward curvature was observed in 8 h. 15 m., but usually not until 24 h. had elapsed.  Although only 9 out of 39 radicles were affected, yet the curvature was so distinct in several of them, that there could be no doubt that the tip is sensitive to slight contact, and that the growing part bends away from the touching object.  It is possible that some secondary radicles are more sensitive than others; for Sachs has proved* the interesting fact that each individual secondary radicle possesses its own peculiar constitution.

Sensitiveness to contact of the Primary Radicle, a little above the apex, in the Bean (Vicia faba) and Pea (Pisum sativum).—­The sensitiveness of the apex of the radicle in the previously described cases, and the consequent curvature of the upper part from the touching object or other source of irritation, is the more remarkable, because Sachs** has shown that pressure at the distance of a few millimeters above the apex causes the radicle to bend, like a tendril, towards the touching object.  By fixing pins so that they pressed against the radicles of beans suspended vertically in damp air, we saw this kind of curvature; but rubbing the part with a twig or needle for a few minutes produced no effect.  Haberlandt remarks,*** that these radicles in breaking through the seed-coats often rub and press against the ruptured edges, and consequently bend round them.  As little squares of the card-like paper affixed with shellac to the tips were highly efficient in causing the radicles to bend away from them, similar pieces (of about 1/20th