528 SENSITIVENESS TO GEAVITATION. CHAT. XI 



caee that when the tips are amputated after an exposure to geo- 

 tropism of only 45 m., though a slight influence is sometimes 

 transmitted to the adjoining part of the radicle, yet this seldom 

 suffices, and then only slowly, to induce even moderately well- 

 pronounced curvature. 



In the previously given experiments on 29 horizontally ex- 

 tended radicles with their tips amputated, only one grew irre- 

 gularly in any marked manner, and this became bowed upwards 

 at an angle of 65. In Ciesielski's experiments the radicles 

 could not have grown very irregularly, for if they had done 

 so, he could not have spoken confidently of the obliteration 

 of all geotropic action. It is therefore remarkable that Sachs, 

 who experimented on many radicles with their tips amputated, 

 found extremely disordered growth to be the usual result. As 

 horizontally extended radicles with amputated tips are some- 

 times acted on slightly by geotropism within a short time, and 

 are often acted on plainly after one or two days, we thought 

 that this influence might possibly prevent disordered growth, 

 though it was not able to induce immediate curvature. There- 

 fore 13 radicles, of which 6 had their tips amputated trans- 

 versely for a length of 1*5 mm., and the other 7 for a length of 

 only 0'5 mm., were suspended vertically in damp air, in which 

 position they would not be affected by geotropism; but they 

 exhibited no great irregularity of growth, whilst observed 

 during 4 to 6 days. We next thought that if care were not 

 taken in cutting off the tips transversely, one side of the stump 

 might be irritated more than the other, either at first or sub- 

 sequently during the regeneration of the tip, and that this 

 might cause the radicle to bend to one side. It has also been 

 shown in Chapter III. that if a thin slice be cut off one side 

 of the tip of the radicle, this causes the radicle to bend from 

 the sliced side. Accordingly, 30 radicles, with tips amputated 

 for a length of 1-5 mm., were allowed to grow perpendicularly 

 downwards into water. Twenty of them were amputated at an 

 angle of 20 with a line transverse to their longitudinal axes ; 

 and such stumps appeared only moderately oblique. The 

 remaining ten radicles were amputated at an angle of about 

 45. Under these circumstances no less than 19 out of the 30 

 became much distorted in the course of 2 or 3 days. Eleven 

 other radicles were similarly treated, excepting that only 1 mm. 

 (including in this and all other cases the root-cap) was ampu- 

 tated ; and of these only one grew much and two others slightly 



