The Supposed Reversal of Geotropic Response 283 
[of the shoot] is to be demonstrated ”; also that “ no upward curvature 
or positive downward curvature in the dark has been observed in 
unvaselined specimens of maize, Stellaria media or sycamore seed¬ 
lings.” The authors also state that unvaselined shoots in a number 
of cases have shown downward curvature in the dark; and again, 
“The treatment with vaseline and darkness also inhibits the growth 
of the stem.” The foregoing statements and quotations from the 
authors are extraordinary. If their use of vaseline inhibited the 
growth of the shoots, how then could the shoots later show geotropic 
curves ? To say that the unvaselined shoots of maize and other 
species in the dark showed no upward curvature is to condemn their 
own methods; for the testimony of fifty years is against them. Maize 
is one of the most common of plants whose seedlings are used for 
laboratory experiment and class demonstration; and, in practice, 
for the demonstration of geotropic curves, the seedlings are grown 
in the dark. Everyone who has worked with plant tropisms knows 
that the shoots of maize and other seedlings turn upward in the dark 
within an hour or two in usual temperatures. 
The last series of experiments was made by Miss Lynn in the 
attempt to bring reversal of geotropic response in seedling stems by 
the use of carbon dioxide in closed chambers. After some trials, 
the author selected Helianthus annuus for the tests. She found that 
a proportion of carbon dioxide of 10 per cent, or over would give 
reversed curves; of 9 to 10 per cent, would give some positive, some 
negative; while a percentage of less than 9 would give only negative 
curves in the shoot. A plate of figures accompanies the text. The 
figures show that the author’s downward bends were not geotropic, 
but were caused by the sagging of elongated, weak, and etiolated 
shoots. The most of the sagging shoots in the figures show an upward 
bend just below the cotyledons, and this is the true geotropic curve— 
a normal, negatively geo tropic curve. A table also accompanies the 
text, and this shows a higher percentage of carbon dioxide for the 
so-called reversals in March than in February—a result that may 
very well be correlated with the relative sun illumination in the two 
months, if the so-called downward curves were only the sagging of 
weak stems. 
Recently Coupin(2) has published the statement that he found the 
seedling shoot of the lentil taking the horizontal position when 
growing in the dark room. Coupin says that the shoot continued in 
its horizontal position till it died. There have been reports by earlier 
writers of similar behaviour by other leguminous seedlings; but all 
these unusual behaviours have been found to be due to the presence 
of illuminating or other poisonous gas. Coupin makes no mention 
of precautions against such disturbing influences. If the shoot of 
