MOVEMENTS OF PLANTS 47 



The plan adopted by us was simply to cut oflf 

 the extreme tip of the roots, and fortunately (or 

 unfortunately) the result was just what was 

 expected — the tipless roots had lost the sense of 

 gravitation, and were unable to curve downwards 

 towards the centre of the earth. It was natural to 

 believe that the tipless roots failed to bend because 

 their sense-organs — their percipient parts — had 

 been removed. As a matter of fact they had been 

 removed, but it was fairly objected that the 

 operation of removing the delicate tissues at the 

 tip of the root is a severe one, and that the roots 

 which refused to grow downwards were suffering 

 from shock, and not from the absence of their sense- 

 organs. 



The subsequent history of the inquiry is an 

 instance of the unwisdom of prophesying unless you 

 know. In 1894 an able summary of the question 

 Was published in a German journal, in which the 

 impossibility of solving the problem of the gravita- 

 tional sensitiveness of the root-tip was dwelt on, 

 and immediately afterwards Section K of the British 

 Association had the satisfaction of hearing Pfeffer 

 read a brilliant paper giving the long-hoped-for 

 proof that the tip of the root is a sense-organ for 

 gravitation.^ 



Like many other experiments, it depends on a 

 deception or trick played on the plant. The root is 

 forced to grow into a minute glass tube closed at 

 one end and sharply bent in the middle, resembling 

 a little glass boot; the extreme tip being thus 



* PfefEer, in the Annals of Botany, September 1894. Further 

 details in Czapek's paper in Pringsheim's Jahrb., 1895. 



