Newcombe, Sensitive Life of Asparagus plumosus. 
39 
2 or 3 days before twining is to begin, tbe twining is wbolly in- 
bibited. Moreover, a sboot that bas already been twining for some 
time may be made to cease twining in 3 days by depriving it of 
ligbt. A sboot tbat bas ceased to twine in tbe dark will, in tbe 
ligbt, regain its ability to twine in 3 or 4 days in summer con- 
ditions. Tbe relinquisbment of twining is brot about by 2 cbanges 
in cireunmutation: 1) Tbe diameter of tbe Circuit is greatly rednced, 
becoming zero wben tbe tip rises to tbe vertical; 2) tbe regulär 
movement of tbe tip of tbe stem cbanges to tbe irregulär nutation 
of an ordinary ortbotropic stem. Tbe case bas its points of re- 
semblance to tbe bebavior of tbe non-twining stem in tbe dark. 
In tbe latter, tbe plagiogeotropism alternates irregularly witb ne¬ 
gative geotropism; wbile witb tbe twining sboots, tbe response to 
gravitation wbicb leads to tbe regulär Circuit of tbe tip cbanges 
in tbe dark irregularly and transitorily to negative geotropism. 
But in tbe twining sboots in tbe dark, tbere is no temporary return 
to circumnutation long enougb to permit one complete Circuit; tbat 
is, tbere is not one complete turn about a support. Tbe access of 
ligbt restores to tbe plant its plagiogeotropism and its circumnu¬ 
tation, but only after tbe lapse of 3 or 4 days. Tbe lengtb of 
tbis restoration period indicates tbat bere, as in tbe case of tbe 
non-twining sboots, tbere are internal processes concerned witb 
tbe establisbment of tbe plagiogeotropism wbicb require considerable 
time for tbeir consummation. 
VII. Biological Significane of the Behavior of Asparagus. 
Tbis Asparagus being in its greatest development a twining 
plant, and twining plants generally in tbeir native babitat baving 
to contend witb tbe sbade of tbe plants wbicb give tbem mecbanical 
support, one migbt wonder tbat tbe twining babit sbould be so 
readily relinquisbed in tbe dark. But it must be remembered tbat 
tbe degree of illumination necessary to insure twining bas not 
been determined; it may be tbat weak ligbt is sufficient. On tbe 
otber band, tbe plant, by growing straigbt instead of coiling, 
travels a considerably greater distance, and tbus, otber tbings being 
equal, Stands a better cbance of gaining tbe ligbt. And, even 
witbout twining, tbe plant may be able to grow up tbru a tbicket 
by tbe aid of its book-iike nodal scales, wbicb, it must be re¬ 
membered, are tbe only appendages well developed on tbe etiolated 
sboot. 
Tbe advantage to tbe plant in cbanging, in tbe dark, its 
normally sbort sboots into vertical sboots of great elongation is too 
apparent to need comment. By tbis process tbe plant converts, 
as far as growtb in tbe dark is concerned, its normally sbort, 
diageotropic sboots, and its normally long, twining sboots into 
sboots of a common babit of growtb, a common appearance, botb 
negatively geotropic and ortbotropic; or, ratber, it sbould be said 
tbat tbe resultant direction of growtb is vertical or nearly so, so 
tbat tbe effect is as tbo negative geotropism dominated tbe bebavior. 
