Geai'. I. PHALAEIS 65 



concluded that they were circiimnutating ; but wc thought it 

 advisable to make the tracing above given. 



Radicles. — Glass filaments were fixed to two short radicles, 

 placed so as to stand almost upright, and whilst bending down- 

 wards through geotropism their courses were strongly zigzag ; 

 from this latter circumstance circumnutation might have been 

 inferred, had not their tips become slightly withered after the 

 first 24 h., though they were watered and the air kept very 

 damp. ^Nine radicles were next arranged in the manner 

 formerly described, so that in growing downwards they left 

 tracks on smoked glass-plates, inclined at various angles between 

 45° and 80° beneath the horizon. Almost every one of these 

 tracks ofiered evidence in their greater or less breadth in dif- 

 ferent parts, or in little bridges of soot being 

 left, that the apex had come alternately into Fig. 52. 



more and less close contact with the- glass. In 

 the accompanying figure (Kg. 52) we have 

 an accurate copy of one such track. In two 

 instances alone (and in these the plates were 

 highly incUned) there was some evidence of 

 slight lateral movement. We presume therefore 

 that the friction of the apex on the smoked 

 surface, little as this could have been, sufficed 



to check the movement from side to side of these ,-, , , 



Zeaviays: track 



dehcate radicles. left on inclined 



Avena saliva (Graminese). — A cotyledon, H smelted glass- 

 inch in height, was placed in front 'of a north- pI"'" ,^^ *'P 

 . . , J .i_ L a 1.-1 O' radicle in 



east wmdow, and the movement of the apex growing down- 

 was traced on a horizontal glass during two wards. 

 dayS; It moved towards the light in a slightly 

 zigzag line from 9 to 11.30 a.m. on October 15th ; it then moved 

 a little backwards and zigzagged much until 5 p.isi., after which 

 hour, and during the night, it continued to move towards the 

 window. On the following morning the same movement was 

 continued in a nearly straight line until 12.40 p.m., when the sky 

 remained until 2.35 extraordinarily dark from thunder-clouds. 

 During this interval of 1 h. 55 m., whilst the light was obscure, 

 it was interesting to observe how circumnutation overcame 

 heliotropism, for the apex, instead of continuing to move towards 

 the window in a slightly zigzag line, reversed its course four 

 times, making two small narrow ellipses. A diagram of this case 

 will be given in the chapter on Heliotropism. 



