Newcombe, Sensitive Life of Asparagus plumosus. 39 



2 or 3 days before twiuing is to begin, the twining is wholly in- 

 hibited. Moreover, a shoot that has already been twining for some 

 time may be made to cease twining in 3 days by depriving it of 

 light. A shoot that has ceased to twine in the dark will, in the 

 light, regain its ability to twine in 3 or 4 days in summer con- 

 ditions. The relinquishment of twining is brot about by 2 changes 

 in circumnutation : 1) The diameter of the circuit is greatly reduced, 

 becoming zero when the tip rises to the vertical; 2) the regulär 

 movement of the tip of the stem changes to the irregulär nutation 

 of an ordinary orthotropic stem. The case has its points of re- 

 semblance to the behavior of the non-twining stem in the dark. 

 In the latter, the plagiogeotropism alternates irregularly with ne- 

 gative geotropism; while with the twining shoots, the response to 

 gravitation which leads to the regulär circuit of the tip changes 

 in the dark irregularly and transitorily to negative geotropism. 

 But in the twining shoots in the dark, there is no temporary return 

 to circumnutation long enough to permit one complete circuit; that 

 is, there is not one complete turn about a support. The access of 

 light restores to the plant its plagiogeotropism and its circumnu- 

 tation, but only after the lapse of 3 or 4 days. The length of 

 this restoration period indicates that here, as in the case of the 

 non-twining shoots, there are internal processes concerned with 

 the establishment of the plagiogeotropism which require considerable 

 time for their consummation. 



VII. Biological Significane of the Behavior of Asparagus. 



This Asparagus being in its greatest development a twining 

 plant, and twining plants generally in their native habitat having 

 to contend with the shade of the plants which give them mechanical 

 support, one might wonder that the twining habit should be so 

 readily relinquished in the dark. But it must be remembered that 

 the degree of illumination necessary to iusure twining has not 

 been determined; it may be that weak light is sufficient. On the 

 other hand, the plant, by growing straight instead of coiling, 

 travels a considerably greater distance, and thus, other things being 

 equal, Stands a better chance of gaining the light. And, even 

 without twining, the plant may be able to grow up thru a thicket 

 by the aid of its hook-like nodal scales, which, it must be re- 

 membered, are the only appendages well developed on the etiolated 

 shoot. 



The advantage to the plant in changing, in the dark, its 

 normally short shoots into vertical shoots of great elongation is too 

 apparent to need comment. By this process the plant converts, 

 as far as growth in the dark is concerned, its normally short, 

 diageotropic shoots, and its normally long, twining shoots into 

 shoots of a common habit of growth, a common appearance, both 

 negatively geotropic and orthotropic; or, rather, it should be said 

 that the resultant direction of growth is vertical or nearly so, so 

 that the effect is as tho negative geotropism dominated the behavior. 



