Sense-Life and Sensibility 
grains are at first irregular, but become regular and like 
statoliths when the older stage is reached." On the 
other hand, when there is a marked reaction, all, with 
very few exceptions, who have looked for statoliths, 
seem to have discovered them. 
The curvature due to gravity occurs rapidly enough, 
for in about two-thirds of a second to a second the 
root begins to curve.” 
The sensitiveness of tendrils and of young roots to 
touch or contact is unmistakable. Something of the 
same nature is found in submerged roots and leaves 
when growing in the rapid current of a river or stream. 
This sort of “tact” is certainly due to some sort of 
“distress” of the protoplasm in the cells affected, at 
least there is a hazy sort of idea that it is due to the 
injury or suppression of growth of the cells immediately 
affected ; no real explanation has as yet been offered. 
Darwin’s passion-flower and other tendrils, which curve 
at once when gently stroked, are the classical examples 
of this reaction, Its use is obvious, and especially in 
the case of roots which have to (so to speak) feel their 
way in and out amongst sharp-edged stones and curving 
passages in the soil. 
But a still more remarkable and impressive example 
of sensitiveness to touch is afforded by the stamens of the 
Barberry, of Mahonia, of some species of Centaurea, and 
of other plants. The sudden jump inwards of the Bar- 
berry stamens, whilst the pollen is simultaneously thrown 
out of its open pore, is one of the most wonderful con- 
trivances for pollination in the whole range of flower 
structure. 
Until recently it was supposed that the movement 
was due to some sudden change in the water contents 
of the epidermis cells. But Professor Heckel made an 
extremely difficult operation on the Mahonia stamens 
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