BEHAVIOR OF ASPARAGUS PLUMOSUS 



63 



traveled through an angle of 180°. As the shoot nears the end 

 of its growth and begins to take the horizontal position, its 

 heliotropisin becomes weaker and weaker. \M\en the lateral 

 branches are nearly full grown, the apex of the main axis re- 

 sponds but feebly or not at all to one-sided illumination. This 

 was demonstrated in several cases by using the dark-box with 

 the small window in one side. The growth of the main axis 

 and of its branches ceases at about the same time; and with 

 this cessation there is no longer any heliotropism shown. 



In a potted plant, the young, positively heliotropic shoot 

 is always deflected shghtly from the vertical by the unequal 

 distribution of light. The transverse position later assumed 

 by the apex of this shoot is always in the direction of the pre- 

 vious inchnation. Thus it can be said of the Asparagus shoot, 

 as Sachs said of other plagiotropic shoots, that the plane of 

 bending is due to positive heliotropism. 



WTiile positive heliotropism may cause the shoot to bend 

 from the vertical, it could never, with the plant unshaded above, 

 cause the bend to go as far as the horizontal. It is conceivable, 

 however, that negative heliotropism might cause the stem to 

 take the horizontal position by the member reversing its re- 

 sponse toward light. That the horizontal position of the apex 

 of the shoot is due neither to negative heliotropism nor to epi- 

 nasty can be shown by the following results: 



1. Pots with young orthotropic shoots which showed no 

 indication of making their transverse bend were placed in the 

 dark-room. The tips later took their horizontal position as 

 though the plants were in normal environment. 



2. Two pots of plants each with an orthotropic shoot which 

 was bending into the horizontal position were selected and the 

 older shoots cut away. These preparations were then revolved 

 on the khnostat for sixty-seven hours. The axis of the klino- 

 stat was horizontal, and the plant was so placed that the plane 

 passing through the straight and the bent portion of the shoot 

 was perpendicular to the axis of the klinostat. The whole shoot 

 of the plant, therefore, described in its revolution a vertical 

 plane. An opaque paper cylinder covered each plant admit- 



