Institut., in W?rzburg,' vol. i. 1872, p. 209.
[page 181]
radicle to bend away from the source of irritation. In our experiments we
followed Sachs' plan, and sieves with seeds germinating in damp sawdust
were suspended so that the bottom was generally inclined at 40o with the
horizon. If the radicles had been acted on solely by geotropism, they would
have grown out of the bottom of the sieve perpendicularly downwards; but as
they were attracted by the adjoining damp surface they bent towards it and
were deflected 50o from the perpendicular. For the sake of ascertaining
whether the tip or the whole growing part of the radicle was sensitive to
the moist air, a length of from 1 to 2 mm. was coated in a certain number
of cases with a mixture of olive-oil and lamp-black. This mixture was made
in order to give consistence to the oil, so that a thick layer could be
applied, which would exclude, at least to a large extent, the moist air,
and would be easily visible. A greater number of experiments than those
which were actually tried would have been necessary, had not it been
clearly established that the tip of the radicle is the part which is
sensitive to various other irritants.
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