CHAP. V. 



EFINASTY AND HYPONASTY. 



273 



extreme part, instead of hang- 

 ing vertically down as would 

 follow if weight was the efficient 

 cause, extends horizontally or 

 even points upwards. A shoot, 

 which terminated in a rather 

 open hook, was fastened in 

 a highly inclined downward 

 position, so that the concave 

 side faced upwards, and the 

 result was that the apex at first 

 curved upwards. This ap- 

 parently was due to epinasty 

 and not to apogeotropism, for 

 the apex, soon after passing 

 the perpendicular, curved so 

 rapidly downwards that we 

 could not doubt that the move- 

 ment was at least aided by 

 geotropism. In the course of 

 a few hours the hook was thus 

 converted into a loop with the 

 apex of the shoot pointing 

 straight downwards. The 

 longer axis of the loop was at 

 first horizontal, but after- 

 wards became vertical. During 

 this same time the basal part 

 of the hook (and subsequently 

 of the loop) curved itself slowly 

 upwards ; and this must have 

 been wholly duo to apogeo- 

 tropism in opposition to hypo- 

 nasty. The loop was then 

 fastened upside down, so that 

 its basal half would be simul- 

 taneously acted on by hypo- 

 nasty (if present) and by apo- 

 geotropism ; and now it curved 

 itself so greatly upwards in 

 the course of only 4h. that 

 there could hardly be a doubt 

 that both forces were acting 



Fig- 122- 



9'JS'cim. 



Ampelopsis tricuspidata ; hyponastic 

 movement of hooked tip of leading 

 shoot, traced from 8.10 A.M. July 

 13th to 8 A.M. 15th. Apex of shoot 

 5g inches from the vertical glass. 

 Plant illuminated through a sky- 

 light. Temp. 17t-19C. Diagram 

 reduced to one-third of original scale. 



