1915] CURRENT LITERATURE 423 
reason his pioneer work should be followed by a similar study of a great variety 
of seeds and fruits —WILLIAM CROCKER. 
Light and growth.—Voct™® has shown that the effect of light upon the 
growth rate of the coleoptile of Avena sativa is very complex, in contrast to the 
older statement that light always inhibits growth. Temporary illumination 
of sufficient intensity is shortly followed by a considerable yet ee which in 
growth rate. This increase is due to the action of light alone, and not to the 
combined action of light and darkness. The initial inhibitory effect of light 
on growth is not due to increased transpiration, as BLAAUW™ suggests. In 
sufficient illumination the rate and total amount of growth of this organ is 
reduced. The greater amount of illumination causes a second inhibitory effect, 
which greatly exceeds the former acceleration, so that the total effect is a 
marked reduction in rate and amount of growth. This total effect of light 
was all that was definitely studied before Jacosi’s® work in 1911. In this 
total effect, like amount of light gives like effect, even within wide variation of 
the intensity and duration factors. For a given reduction in growth, /ight 
intensityX duration of illumination is a constant. This is the quantity of 
stimulus law which has been shown to have rather general application in 
growth and movement stimuli in plants. It seems then that there are three 
effects of light: inhibition, followed by a greater acceleration upon 
temporary illumination, and a second inhibition largely determining the total 
effect in long or enduring illumination of sufficient strength. These results 
tally in general with those of BLAauw on sporangiophores of Phycomyces, 
except that BLaauw has not found important the initial inhibitory effect of 
light. 
While all the work of Jacosr, BLaauw, and Vocrt will greatly modify the 
statements current in our texts, there is one set of experiments by Voct which 
is especially interesting in this respect. When the organ was alternately 
illuminated (100 M.K. or less) and darkened in 15, 30, or 60-minute periods, 
the illuminated periods gave less growth only in the 30 and 60-minute periods, 
and not in the 15-minute periods. In the longer periods, Voct has shown that 
the greater growth in darkness is due largely to the stimulation effect of the 
previous illumination, and the slower growth in light is not due in the main to 
inhibitory effect of light. This quite reverses the former interpretation given 
to such results. 
Red light acts as very weak diffuse light. This tallies with the known 
existence in the red of photo-stimulation power. A sudden change of 1o-12° C. 
in the temperature has effects very similar to temporary illumination. This 
leads Vocr to inquire whether the effect of temporary illumination is not due 
* Voct, E., Uber den Einfluss des Lichts auf das Wachstum der Koleoptile von 
Avena pane ar aoe Bot. 7:193-270. 1915. 
7 Bor. Gaz. 59:67-68. 1915. 
