The Supposed Reversal of Geotropic Response 285 
poured in of the same strengths, the seedlings kept erect for 5 to 24 
hours, and the jars then turned over so as to bring the seedlings 
into the horizontal position. Of course, it was not necessary to turn 
the seedlings horizontally for the test; for, if the response were 
reversed by the acid, the stems would turn from the erect position 
themselves. 
The experiments ran from 24 hours to five days. There was not 
one reversal of geotropic response. In the chambers with vapour 
from 1 per cent, and those with vapour from 5 per cent, acid, the 
upward curvature of shoots was normal for three days in the seedlings 
suspended in air and those growing in earth. In the experiments 
continued for more than three days in the weaker vapours, the shoots 
became long and sagged, but the resulting bends were near the bases 
of the shoots in Pisum and not near the tip as they would have been 
if geotropic. Many roots lived for two to three days in the vapours 
from concentrations below 10 per cent., but were killed in one day 
in the vapour from the 10 and 20 per cent. acid. In the two stronger 
vapours, both roots and shoots were killed; but most shoots lived 
long enough to make an upward curvature of 20 to go°. 
Series II. Shoots vaselined. The work of Small and Rea in 
smearing the stems of seedlings with vaseline to cause thereby the 
carbon dioxide to accumulate within, and thereby the stems to 
become acid was repeated except that in the present case other 
species were used except for Zea mais. However, one may safely 
assume that the behaviour of most plants will be the same with the 
vaseline treatment. Eighty seedlings of Zea mais were used, 37 of 
Avena sativa L., 56 of Lupinus albus L., 32 of Pisum sativum , 14 of 
Vida faba L., 15 of Cucurbita maxima Duchesne, and 100 of Heli- 
anthus annuus L. 
Smearing the shoots with vaseline or olive oil is very injurious 
to the plant, as recognised by Small and Rea, who say that the growth 
of their plants was thereby inhibited. It is singular that these authors 
should also say that it was necessary to allow their plants to stand 
vertically in the dark from two to seven days, after applying the 
vaseline, before the plants were turned horizontally. In the work 
of Miss Haire and myself, it was found that the plant shoots very 
soon became translucent, after applying the vaseline, except in the 
cases of Avena and Zea . These shoots, being protected by their 
wrappings of leaves, were not penetrated so quickly by the oil, and 
generally made negatively geotropic curves, provided they were 
turned horizontally within 36 hours of the application of the vaseline. 
The shoots of the other species, if they were very young—1 to 3 cm. 
long—showed initial upward curves, but their growth and movement 
soon ceased. If the shoots were longer—8 to 10 cm.—before applying 
