Botany; Geotropism; Plants -- Irritability and movements
A younger and shorter stolon was supported so that it projected at
about 45° above the horizon, and its movement was traced by the same
orthogonal method. On the first day the apex soon rose above the field
of vision. By the next morning it had sunk, and the course pursued was
now traced during 14 h. 30 m. (Fig. 87). The amount of movement was
almost the same,
from side to side as up and down; and differed in this respect
remarkably from the movement in the previous cases. During the latter
part of the day, viz., between 3 and 10.30 P.M., the actual distance
travelled by the apex amounted to 1.15 inch; and in the course of the
whole day to at least 2.67 inches. This is an amount of movement almost
comparable with that of some climbing plants. The same stolon was
observed on the following day, and now it moved in a somewhat less
complex manner, in a plane not far from vertical. The extreme amount of
actual movement was 1.55 inch in one direction, and .6 inch in another
direction at right angles. During neither of these days did the stolon
bend downwards through geotropism or its own weight.
Fig. 87. Fragaria: circumnutation of another and younger stolon, traced
from 8 A.M. to 10.30 P.M. Figure reduced to one-half of original scale.
Four stolons still attached to the plant were laid on damp sand in the
back of a room, with their tips facing the north-east windows. They
were thus placed because De Vries says[3] that they are apheliotropic
when exposed to the light of the sun; but we could not perceive any
effect from the above feeble degree of illumination. We may add that on
another occasion, late in the summer, some stolons, placed upright
before a south-west window
on a cloudy day, became distinctly curved towards the light, and were
therefore heliotropic. Close in front of the tips of the prostrate
stolons, a crowd of very thin sticks and the dried haulms of grasses
were driven into the sand, to represent the crowded stems of
surrounding plants in a state of nature. This was done for the sake of
observing how the growing stolons would pass through them. They did so
easily in the course of 6 days, and their circumnutation apparently
facilitated their passage. When the tips encountered sticks so close
together that they could not pass between them, they rose up and passed
over them. The sticks and haulms were removed after the passage of the
four stolons, two of which were found to have assumed a permanently
sinuous shape, and two were still straight. But to this subject we
shall recur under Saxifraga.
[3] ‘Arbeiten Bot Inst., Würzburg,’ 1872, p. 434.
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