Sense-Life and Sensibility 
a way that it grows horizontally at right angles to the 
force of gravity.2 So guided by light and gravity, the 
Solomon’s seal discovers the precise depth at which it 
is adapted to grow. It must be remembered that such 
stimuli as these are not necessarily motive forces, 
They may be used like the mariner’s compass which 
guides a ship across the ocean, and need not be com- 
pared to the steam which drives its engines. 
It has been found by careful and minute investigation 
that in those parts of plants which show themselves 
sensitive to the action of gravity, there are almost always 
numbers of small starch grains called stafoliths. Suppose 
that in the cells of a root the protoplasm is only 
“happy” when these starch grains are resting on the 
lowest wall or floor of the cell. If the root is sup- 
posed to be tilted sideways, then the grains will drop 
into a corner of the cell. The protoplasm is supposed 
to react to this uncomfortable condition, and by the 
growth of the cell or movements of the cell contents 
bring the cell back into the right position. To do this 
the root turns or grows downwards. 
The similarity of this reaction to that of the otoliths 
in the ears of the higher animals is very remarkable, 
and in spite of the complex nature of the whole pro- 
ceeding most recent authorities seem to believe that it 
is by the tumbling about of these starch-grains on a 
sensitive protoplasmic layer that both stems and roots 
react to gravity. 
Some of the evidence is very strong. Thus in the 
roots of parasites, and in those of certain arums, willows, 
and other water plants which do not show the usual 
downward growth, there are no such statoliths.® In 
some grasses (Festuca sp. and Poa sp.) the seedlings 
show at first no geotropy, but when they are mature 
there is a marked reaction, In those roots the starch 
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