Botany; Geotropism; Plants -- Irritability and movements
We succeeded better in ascertaining the force exerted transversely by
these radicles. Two were so placed as to penetrate small holes made in
little sticks, one of which was cut into the shape here exactly copied
(Fig. 55). The short end of the stick beyond the hole was purposely
split, but not the opposite
end. As the wood was highly elastic, the split or fissure closed
immediately after being made. After six days the stick and bean were
dug out of the damp sand, and the radicle was found to be much enlarged
above and beneath the hole. The fissure which was at first quite
closed, was now open to a width of 4 mm.; as soon as the radicle was
extracted, it immediately closed to a width of 2 mm. The stick was then
suspended horizontally by a fine wire passing through the hole lately
filled by the radicle, and a little saucer was suspended beneath to
receive the weights; and it required 8 lbs. 8 ozs. to open the fissure
to the width of 4 mm.—that is, the width before the root was extracted.
But the part of the radicle (only .1 of an inch in length) which was
embedded in the hole, probably exerted a greater transverse strain even
than 8 lbs. 8 ozs., for it had split the solid wood for a length of
rather more than a quarter of an inch (exactly .275 inch), and this
fissure is shown in Fig. 55. A second stick was tried in the same
manner with almost exactly the same result.
Fig. 56. Wooden pincers, kept closed by a spiral brass spring, with a
hole (.14 inch in diameter and .6 inch in depth) bored through the
narrow closed part, through which a radicle of a bean was allowed to
grow. Temp. 50°–60° F.
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