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288 THE WILL IN NATURE.
changed every day, a stick fixed upright; within six inches
of a young convolvulus is sure to be found by the plant.
If, after having wound itself for a certain distance round
the stick, it is unwound and wound round again in the
opposite direction, it will return to its original position
or lose its life in the endeavour to do so. Nevertheless,
if two such plants grow close to one another without
having any stick near enough for them to cling to it,
one of them will change the direction of its winding and
they will twine round each other. Duhamel placed some
Italian beans in a cylinder filled with moist earth ; after a
little while they began to germinate and naturally sent
their plumula upwards in the direction of the light and
their radicula downwards into the mould. After a few
days the cylinder was turned round to the extent of a
quarter of its circumference and the same process was
repeated until it had been turned completely round. The
beans were then removed from the earth, when it was
found that both plumula and radicula had twisted at
each turn that had been given, in order to adapt them
selves to it, the one endeavouring to rise perpendicularly,
the other to descend, so that they had formed a complete
spiral. Yet, notwithstanding this natural tendency to
descend, when the soil below is too dry, roots will grow
upwards in order to reach any moist substance which may
be lying higher than themselves."
In Froriep s
"
" Memoranda for 1833 (No. 832) there is
a short article upon the locomotivity of plants : in poor
soil, where good mould lies near at hand, many plants will
send out a shoot into the good mould ; after a time the
original plant then withers, but the offshoot prospers and
itself becomes the plant. By means of this process, a
plant has been known to climb down from a wall.
In the same periodical (1835, No. 981) is to be found a
communication from Professor Daubeny, of Oxford (taken