Newcombe, Sensitive Life of Asparagus plumosus. 37 



shoots when restored to the light after weeks or months in the 

 dark. It has already been said that the position normally assumed 

 by the shoots when growing in the light is the horizontal, and 

 that etiolated shoots in the dark, as a rule, descend to an angle 

 considerably above the horizontal, alternating up and down between 

 the vertical position and a cleclination of 15°to45°. On removing 

 these etiolated plants to the light, diffused light because direct 

 would be injurious in sunimer, they invariably lift their apex 10° 

 to 30° after the lapse of 8 to 36 hours, then nutate narrowly up 

 and down for 2 to 5 days, and then begin the rapid decline to 

 the horizontal from which there is no return. Meantime, the 

 branches begin to grow out, and growth of the main apex slows 

 down. In watching the behavior of these plants, one cannot escape 

 the conviction that the plagiogeotropism of the shoot in the dark 

 is of a somewhat different quality from the plagiogeotropism of the 

 shoot in the light. It might be more correct to say that the in- 

 ternal conditions surrounding the plagiogeotropism must be different 

 in the two cases. Plagiogeotropism in the light is intimately 

 associated with cessation of growth; in the dark, growth proceeds 

 unchecked. The assumption of the transitory plagiotropic position 

 in the dark is hesitating and variable; the movement to the pla- 

 giotropic position in the light is unhesitating and unvarying. One 

 recognizes the phenomenon as a distinct change in behavior. 



IV. Light as Related to Cessation of Growth. 



Many times in the present paper the Statement has been 

 made that, if the shoots from the rhizomes are covered from the 

 light early enough, these shoots have an indefinite elongation. 

 These etiolated shoots not only have longer internodes than those 

 growing in the light, but they have been raised with 7 times as 

 many internodes as a normally growing shoot would have, and 

 elongatiou was not then ended. It must be therefore that light 

 acts as an inhibiting influence on growth, and in the absence of 

 the inhibiting agent elongation finds no hindrance. Light alone, 

 without the action of gravitation, is the inhibiting agent; for, on 

 the klinostat in the light, a young shoot revolved about its axis 

 laid horizontally ends its elongation as readily as when growing 

 at rest. That the taking of the plagiotropic position is not the 

 Stimulus for cessation of growth is shown by the klinostat experi- 

 ment in which growth ceased without a bend of the stem and 

 without developing diageotropism. The inhibiting effect of light, 

 however, is not direct. Changes are set in Operation which con- 

 tinue to act for days after light is cut off. In the experiments 

 cited in an earlier part of this paper the retardation of growth 

 was not marked for at least 8 days, and the cessation did not 

 occur for at least 12 days after light was excluded. 



