Manito eBooks

Then
geotropism prevailed and caused the apex to grow perpendicularly downwards.
In another case, shown at (D), the apex
Fig. 69. Zea mays: radicles excited to bend away from the little squares of
card attached to one side of their tips.
in making a second turn or spire, passed through the first loop, which was
at first widely open, and in doing so knocked off the card; it then grew
perpendicularly downwards, and thus tied itself into a knot, which soon
became tight!
Secondary Radicles of Zea.--A short time after the first radicle has
appeared, others protrude from the
[page 180]
seed, but not laterally from the primary one. Ten of these secondary
radicles, which were directed obliquely downwards, were experimented on
with very small squares of card attached with shellac to the lower sides of
their tips. If therefore the squares acted, the radicles would bend upwards
in opposition to gravity. The jar stood (protected from light) on a
sand-bath, which varied between 76o and 82o F. After only 5 h. one appeared
to be a little deflected from the square, and after 20 h.


Pages:
289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313