Newcombe, Tliigmotropism of terrestrial roots. 63 



attached to the side of tlie root-tip would give a negative curve. 

 Spalding^) attached thin scales of glass and of mica to the 

 roots of 19 Vicia faha seedlings, „just back of the apex'^, and 

 and no curves followed. As will be seen in the following pages, 

 my own resnlts agree with these, except in the case of the thin 

 glass scales used by Detlef sen. 



The first series of experiments was carried through by attach- 

 ing to the sloping side of the root-tips of Pismn sativum L. 

 little Squares of filter-paper , blotting paper, thin white linen 

 paper, and white cardboard, all -of wdiich were washed in water 

 for hours before using. The bits of paj^er were from 2 to 4 mm 

 Square, the larger pieces giving the more pronounced results. 

 In general it may be said that the responses in a temperature 

 of 18 " to 20 " C. come in 6 to 12 hours. Over a hundred seed- 

 lings of P/suvi have been tlius treated, and over half of them 

 have given strongly negative bends ; the record shows only 4 

 roots with positive curves. The following are examples of 3 

 representative experiments in Avliich Squares of filter-paper were 

 attached to one side of the root-tip : Among 5 roots , 4 became 

 negative and one j^ositive; among 8, 2 became negative and 6 

 remained straiht; among 20, 11 became negative and 9 remained 

 straight. As examjjles of experiments in which bits of white 

 cardboard were attached to the root-tips , these are given : among 

 30 seedlings of Pisum^ 29 roots became negative and one posi- 

 tive; among 28 seedlings, 27 became negative and one remained 

 straight. The results when blotting paper and when white linen 

 paper were used were similar to the foregoing. Lupinus albus 

 L., Fagopyrum esculentum^ and Brassica alba gave results differ- 

 ing in no way from those shown by Pisum sativum. 



Before interpreting these results as negative thigmotropism, 

 one must guard against errors through hydrotopism, traumatro- 

 pism, and possibly chemotropism. That the results could not 

 be due to the withdrawal of water from the root by the paper 

 was shown by 3 modifications of the experiment. The damp- 

 chamber was given a very great evaporating siu'face by almost 

 tilling the space not occupied by the seedlings with folds of 

 absorbent paper. In the second place, in each preparation, some 

 of the roots had dry paper attached, while alternating roots had 

 water saturated paper attached. In the third modification, a little 

 reservoir of water was set above the seedlings and water was 

 conducted by a thread down to the bit of wet paper hanging 

 to the root. None of these modifications had any effect on the 

 result: the negative curves came as before. 



It is perhaps conceivable that all these papers received from 

 the method of manuf acture something injuinous to the roots, though 

 this would be imjDrobable for the filter-paper used. Accordingiy 



1) Spalding, Tlie traiTmatropic curvature of roots. (Ann. of Bot. 

 Vin. 429.) 



