N e w c o mb e , Tliigmotropism of terrestrial roots. 75 



a half of each revolution , and possibly cause a response by the 

 intermittent Stimulation. Ten seedling-s of Pisiim sativum thus 

 treated gave no response during a period of 8 hours, in a tem- 

 perature of 25 " C. Four seedlings of Fagopyrum esculentwn in 

 similar conditions showed, after 3 liours, 3 roots positive and 

 one neutral. Twenty-five seedlings of Bajihamis sativiis in sim- 

 ilar treatment for periods varying from one and one half to 

 six and one half hours showed 4 roots positive, one negative, 

 and 20 neutral. From these results it is evident that the roots 

 used (with the exception of Fagopyrum. of which too few seed- 

 lings were tested) are not thigmotropic, or that this kind of an 

 intermittent pressure is not appropriate Stimulation. 



In the next series of experiments, continuous pressure was 

 exerted on the elongating zone by bringing against it a glass 

 rod thrust into the cork floor of the damp-chamber, the rods 

 being drawn out at one end for easy insertion into the cork. 

 The species (or varieties) used with their reactions were Zea mays 

 (white dent), 22= +,2== — , 23 =0; Zea mays (popcorn), 

 62 = -j- ? ^ = — 1 30 = ; Bicinus communis L., 6 = -|- , 3 = — , 



2 =^ 0; Tropaeolum majus L., 13 = -j-, 10 = 0; Cucurbita pepo 

 L., 3 =: -f-i 3 = — , 12 = 0; Cucumis meto 1j.^ 11 = -|-, 6 = — , 

 30 = 0; Fagopyrum esculentum, 27 = -\-, 18 = 0; Helianthus 

 annuus L., 21 =^ -|-, 5 = — , 19 = 0; Pisum sativum^ Iß = -f, 



3 = — , 23 = 0; Lupimis albus, 19 = +, 2 = — , 17 = 0; 

 Vicia faba^ 10= -f, 3 = — , 4 = 0; Glycine hispida Maxim., 

 1 ^ — . 13 = 0, Lathyrus odoratitslL.^ 18 = +, 6 = — , 10 = 0; 

 Phaseolus vulgaris^ 13=+, 3 = — , 11 =0; Brassica alba, 

 30 = +,11 ^= — ^,8 = 0; Brassica oleracea L. , 38 = + , 12 = — , 

 29 = 0; Bap)ha}ius sativus, 45 = +, 4 = — , 14 = 0. Unlike 

 the disappointing and uncertain showing of reactions in former 

 experiments, we have here pronounced curves in large enough 

 Proportion in all except three species to Warrant one in accept- 

 ing them as irritable responses to the presence of the glass- 

 rods. From the fact that in the experiments already described 

 in which bits of glass were laid on the elongating zone, and in 

 other experiments in which wet bits of filter paper were simi- 

 larly placed, tliere had generally been no response when the 

 seedlings were revolved on the klinostat, the responses following 

 the use of glass rods in the last series were regarded as prob- 

 ably thigmotropic. Moreover the damp-chambers revolved on 

 the klinostats were very moist, probably saturated with moisture 

 at the outset, and physiologists do not look for hydrotropic re- 

 actions in very moist Chambers. This belief in the final appear- 

 ance of the much sought thigmotropism, accounts for the large 

 number of species and individuals employed. Contemplation of 

 conditions however brought disquieting doubt as to whether hy- 

 drotropism had not played a part in inducing the curves. The 

 sloping tips of the roots did not lie in contact with the glass- 

 rods, but might there not be a diffusion of moisture from the 

 rods to the tips, even in a very moist Chamber? If not this. 



