sand, on which four smoked glass-plates rested, inclined at angles of 70o
and 65o with the horizon. The tips of the radicles were placed so as just
to touch the upper end of the glass-plates, and, as they grew downwards
they pressed lightly, owing to geotropism, on the smoked surfaces, and left
tracks of their course. In the middle part of each track the glass was
swept clean, but the margins were much blurred and irregular. Copies of two
of these tracks (all four being nearly alike) were made on tracing paper
placed over the glass-plates after they had been varnished; and they are as
exact as possible considering the nature of the margins (Fig. 18). They
suffice to show that there was some lateral, almost serpentine movement,
and that the tips in their downward course pressed with unequal force on
the plates, as
[page 29]
the tracks varied in breadth. The more perfectly serpentine tracks made by
the radicles of Phaseolus multiflorus and Vicia faba (presently to be
described), render it almost certain that the radicles of the present plant
circumnutated.

Fig. 18. Aesculus hippocastanum: outlines of tracks left on inclined
glass-plates by tips of radicles. In A the plate was inclined at 70o with
the horizon, and the radicle was 1.9 inch in length, and .23 inch in
diameter at base. In B the plate was inclined 65o with the horizon, and the
radicle was a trifle larger.

Phaseolus multiflorus (Leguminosae).--Four smoked glass-plates were
arranged in the same manner as described under Aesculus, and the tracks
left by the tips of four radicles of the present plant, whilst growing
downwards, were photographed as transparent objects. Three of them are here
exactly copied (Fig. 19). Their serpentine courses show that the tips moved
regularly from side to side; they also pressed alternately with greater or