452 PHYSIOLOGY OF GROWTH. 



175. The Function of the Root Tip in Connection with Geotropic 



Curvatures. 



As is well known, it was asserted with great positiveness by 

 Darwin that ihe root tip is of essential importance in connection 

 with the production of geotropic curvatures in the root. 1 For 

 this and other reasons he speaks of a "brain function" of the 

 root tip, certainly an unfortunate expression, which may very 

 readily lead to misconception. The question raised by Darwin, 

 which, however, had already been investigated by Ciesielski and 

 Sachs, has given rise to numerous researches, the results of which 

 are partly for and partly against his view. a Seedlings of Pisum, 

 Zea, Vicia Faba, or Phaseolus serve best for our experiments. 

 After being soaked the seeds are germinated in moist sawdust 

 until their roots, growing vertically downwards, have attained a 

 length of 23 cm. Some of the roots (it is best to use a good 

 number, say twenty) are now marked with ink lines at a distance 

 of 15-20 mm. from the apex, and half of the seedlings are placed 

 in moist sawdust with their roots directed horizontally. In the 

 case of the remaining seedlings we remove the root tip to a length 

 of 1*5-2 mm., by placing the root on a sheet of cork, and with a 

 sharp razor cutting off transverse slices as nearly as possible at 

 right angles to the root until the desired result is attained. The 

 seedlings with the decapitated roots are now also laid horizontally 

 in moist sawdust. After twenty-four to forty-eight hours we 

 determine the amount of growth in all the seedlings, and observe 

 whether they have performed geotropic curvatures. I found in 

 experiments with Phaseolus multinorus that the normal roots in 

 the course of forty-eight hours had all made far greater growth 

 than the decapitated ones. The root tips had been removed to 

 a length of 2 mm. This result does not, however, harmonise 

 with the statements of all, though certainly with those of some 

 observers who have investigated the matter. My experiments 

 with Phaseolus showed, moreover, that the roots of the intact 

 plants executed normal geotropic curvatures, but that the curva- 

 tures made, it is true, by the decapitated roots were in different 

 directions, sometimes upwards, sometimes sideways, or again 

 downwards. 



I am far from wishing to draw from my observations conclu- 

 sions respecting the function of the root tip in connection with 

 geotropic curvatures, since my experiments with Phaseolus, and 



