524 SENSITIVENESS TO GRAVITATION. CHAP. XI. 



vegetative point) of the tips of the radicles of the 

 bean (Vicia fdba), and placed them horizontally or 

 vertically in damp air, earth, and water, with the 

 result that they became bowed in all sorts of direc- 

 tions.* He therefore disbelieved in Ciesielski's con- 

 clusions. But as we have seen with several plants 

 that the tip of the radicle is sensitive to contact and 

 to other irritants, and that it transmits some influence 

 to the upper growing part causing it to bend, there 

 seemed to us to be no a priori improbability in 

 Ciesielski's statements. We therefore determined to 

 repeat his experiments, and to try others on several 

 species by different methods. 



Vicia f aba. Eadicles of this plant were extended horizontally 

 either over water or with their lower surfaces just touching it. 

 Their tips had previously been cut oil", in a direction as accu- 

 rately transverse as could be done, to different lengths, measured 

 from the apex of the root-cap, and which will be specified in 

 each case. Light was always excluded. We had previously 

 tried hundreds of unmutilated radicles under similar circum- 

 stances, and found that every one that was healthy became 

 plainly geotropic in under 12 h. In the case of four radicles 

 which had their tips cut off for a length of 1*5 mm., new root- 

 caps and new vegetative points were re-formed after an interval 

 of 3 days 20 h. ; and these when placed horizontally were acted 

 on by geotropism. On some other occasions this regeneration 

 of the tips and reacquired sensitiveness occurred within a some- 

 what shorter time. Therefore, radicles having their tips 

 amputated should be observed in from 12 to 48 h. after the 

 operation. 



Four radicles were extended horizontally with their lower 

 surfaces touching the water, and with their tips cut off for a 

 length of only 0'5 mm. : after 23 h. three of them were still 

 horizontal ; after 47 h. one of the three became fairly geotropic ; 

 and after 70 h. the other two showed a trace of this action. The 

 fourth radicle was vertically geotropic after 23 h. ; but by an 



' Arbeiten des Bot. Institute in AViirzburg,' Heft. iii. 1873, p. 432. 



