GROWTH OF ROOTS 



Have they some extraordinary sense of the direction of 

 the points of the compass ? It is said that if a side root, 

 which is growing, say for instance downwards and west- 

 wards, is turned in some other direction, it will after a 

 time resume its original westerly voyage. This fact is a 

 most extraordinary one, if true, but it can scarcely be said 

 that it has been proved, and, as will be shown later, there are 

 other curious facts in the behaviour of roots which might 

 explain the experiment without assuming that roots know 

 the points of the compass. 



If one cuts a branch of willow and plants it upside down 

 in the earth, it will very likely take root and grow. Its ap- 

 pearance will be most extraordinary, for the roots will grow 

 downwards, whilst the branches, instead of growing in the 

 direction of the old branches, turn round and grow up- 

 wards.^ 



Why do roots generally grow downwards ? The fact is so 

 familiar that the difficulty of answering does not, at first 

 sight, seem so great as it really is. 



Pfeffer, the great physiologist, has the following interesting 

 comparison. Suppose a man is trying to find his way in the 

 dark, then a single lingering ray of light gives him an im- 

 pulse to walk towards it.^ So our root, also in the dark, 

 feels the pull of gravity and endeavours to grow downwards. 

 Others have compared the direction of gravity to the 

 sailor's compass, and suppose that the root is guided in the 

 same sort of way. 



But a young, vigorous root making or forcing its way in 

 darkness through stones and heavy earth is a most interesting 

 and fascinating study. 



1 Kerner and Oliver, I.e., vol. 1, p. 88. 



2 Ammls of Botany , 1904. 



88 



