37 
Newcombe, Sensitive Life of Asparagus phimosus. 
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 np and down between 
the vertical position and a declination of 15°to45°. On removing 
these etiolated plants to the light, diffused light because direct 
would be injurious in summer, they invariably lift their apex 10° 
to 30° after the lapse of 8 to 36 hours, then nutate narrowly np 
and down for 2 to 5 days, and then begin the rapid decline to 
the horizontal from which there is no return. Heantime, 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 conyiction 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, bnt they have been raised with 7 times as 
many internodes as a normally growing shoot would have, and 
elongation 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. 
