Sense-Life and Sensibility 



grains are at first irregular, but become regular and like 

 statoliths when the older stage is reached. 11 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. 12 



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 



148 



