76 N e w c m b e , Tlügmol ropisni of terrestrial roots. 



iniglit not tlie capillary \vatGi', lield between root and rod, act 

 as a liydrotropic Stimulus , even thougli relations liere would seem 

 to be about the same as in the f'ormer series of experiments in 

 wliicli the capillary water between the bits of glass and the 

 elongating zone did not produce curvature? 



To determine first the possible participatioji of the w^ater 

 held between the root and the glass-post in causing the curva- 

 tures, experiments were set up in which a piece of wet filter- 

 paper 2 mm square was laid on the elongating zone just op]')o- 

 site the glass-post. In other similar preparations, a strip of thin 

 rice paper was wrapped around the elongating zone, the tip of 

 the root not being covered, and the cylinder of paper inter- 

 vening between root and glass-post. It was thought that the 

 paper would distribute the water so nearly equally around the 

 root, that there could be no louger the one-sided influence of 

 liquid water. When however the preparations were made and 

 revolved on the khnostat, curves came as before. Among 45 

 seedlings of Baplianus sativii.s- so treated, 23 became positive, 8 

 negative, and 14 grew straight; and among 14 seedlings of 

 Vicia sativa L., 9 became positive and 5 grew straight. 



If the curving is not to be attributed to the presence of 

 liquid water between the root and the glass-post, we will ex- 

 periment to see whether the glass-post may not have induced hy- 

 drotropism by diffusiug moisture against the root-tip. The tip 

 of the root it will be remembered , in these experiments always 

 extended free f rom the glass-post , but with its sloping ilank not 

 more than ono to three millimeters distant from the glass, Prep- 

 arations quite similar to tliose preceding were made, with a 

 glass-post as before pressing against the elongating zone of each 

 root. Over the tip of each root was set a hood of thin rice 

 paper, the hood covering the apex and the elongating zone, 

 and therefore intervening between root and glass-post. The 

 paper was but one layer in thickness and could not mechanically 

 interfere to any great extent with the curvature of the root. The 

 following species were tested by the foregoing method and 

 gave the results indicated, the temperature being 22 '^ to 23 '^, 

 and the duration of the experiments from 5 to 9 hours: Zea 

 mays (popcornj 8=^ -j-j 3 = - — , 18 = 0; Zea mays (white dent) 

 5 = -|-? 37 = 0; Brassica alba 3=+? 1 = — ? 6=^0. Bras- 

 sica oleracea 9 = -f-? 1 = — ? 16 = 0; Raphanus sativus 15 = -f"? 

 2 = ^ — •, 5 = 0. That the presence of the paper hood over the 

 root-tip served to reduce the number of curvatures there can be 

 no doubt. Controls without the paper hood running at the same 

 time as the foregoing experiments, gave with BopJianus sativus 

 13 ])ositive roots out of a total of 16, with Zea mays (popcorn) 

 18 positive- out of a total of 25, and with Zea mays (white dent) 

 10 positive roots out of a total of 20. Yet in the experiments 

 in which the paper hoods were used, there were proportionaly 

 too many positive cm'ves compared with the negative ones to be 

 ascribed to „accident'^ To my mind this is the best evidence 



