492 LIFE MOVEMENTS^ IN PLANTS 



positivity. The same reversal under condition of snb-toai- 

 city was also shown to take place in growth, where under 

 the stimulus of light a positive acceleration took place, 

 instead of normal retardation of growth (p. 221). In the 

 present investigation, the insensiti7e specimens were found 

 to give abnormal positive electric response to the stimulus 

 of prick made by the probe. The prick-effect in fact often 

 gave me previous indication as to the suitability of the 

 particular specimen for exhibition of geo-electric response. 



Test of ijeotroijic reaction: Experiment 188. — I took four 

 different specimens of Bryophyliiun and Nymplicea, and 

 held them horizontal. These plant organs had, earlier in 

 the season, exhibited very strong geotropic effect, the shoot 

 carving up through 90^ in the course of len hours or les.-j* 

 But these specimens obtained later in the season exhil)ited 

 very feeble curvature, which hardly amounted to 10 ' 

 degrees, even after prolonged exposure to geotropic action 

 for 24 hours. 



Test of microscopic examination. — I next made sections 

 of Bryophytlum and Nympluea and on examining 

 them under the microscope discovered certain striking 

 changes. A fortnight ago the group of large starch grains 

 stained with iodine were the most striking feature of the 

 starch sheath. But now these starch grains could not be 

 found in any of the numerous specimens examined. The 

 presence of the starch grains thus appears to ba associated 

 with the sensitiveness of the perceptive layer. 



REACTION AT LOWER SIDE OF THE ORGAN. 



There remains now the important question or" the 

 physiological change induced on the lower side of the 

 horizontally laid shoot. The physiological reaction of two 

 sides of the organ must be different, since the upper 

 side exhibits contraction and the lower side expan- 

 sion. It may be urged that the effect of one of the 



