Fig. 19.  Phaseolus multiflorus:  tracks left on inclined smoked glass-plates by tips of radicles in growing downwards.  A and C, plates inclined at 60o, B inclined at 68o with the horizon.

Vicia faba (Common Bean) (Leguminosae).—­Radicle.—­Some beans were allowed to germinate on bare sand, and after one had protruded its radicle to a length of .2 of an inch, it was turned upside down, so that the radicle, which was kept in damp air, now stood upright.  A filament, nearly an inch in length, was affixed obliquely near its tip; and the movement of the terminal bead was traced from 8.30 A.M. to 10.30 P.M., as shown in Fig. 18.  The radicle at first changed its course twice [page 30] abruptly, then made a small loop and then a larger zigzag curve.  During the night and till 11 A.M. on the following

Fig. 20.  Vicia faba:  circumnutation of a radicle, at first pointing vertically upwards, kept in darkness, traced on a horizontal glass, during 14 hours.  Movement of bead of filament magnified 23 times, here reduced to one-half of original scale.

morning, the bead moved to a great distance in a nearly straight line, in the direction indicated by the broken line in the figure.  This resulted from the tip bending quickly downwards, as it had now become much declined, and had thus gained a position highly favourable for the action of geotropism.  Fig. 21.  Vicia faba:  tracks left on inclined smoked glass-plates, by tips of radicles in growing downwards.  Plate C was inclined at 63o, plates A and D at 71o, plate B at 75o, and plate E at a few degrees beneath the horizon. [page 31]

We next experimented on nearly a score of radicles by allowing them to grow downwards over inclined plates of smoked glass, in exactly the same manner as with Aesculus and Phaseolus.  Some of the plates were inclined only a few degrees beneath the horizon, but most of them between 60o and 75o.  In the latter cases the radicles in growing downwards were deflected only a little from the direction which they had followed whilst germinating in sawdust, and they pressed lightly on the glass-plates (Fig. 21).  Five of the most distinct tracks are here copied, and they are all slightly sinuous, showing circumnutation.  Moreover, a close examination of almost every one of the tracks clearly showed that the tips in their downward course had alternately pressed with greater or less force on the plates, and had sometimes risen up so as nearly to leave them for short intervals.  The distance between the extreme right and left positions of the radicle A was 0.7 mm., ascertained in the same manner as in the case of Phaseolus.