1910] CROCKER, KNIGHT, ROBERTS—PEG OF CUCURBITS 325 
sized that reliable conclusions can be drawn only by the employ- 
ment of a large number of seedlings in each culture. 
It is evident that both Francis DARWIN and Nott considered 
gravity as well as the arching of the hypocotyl as direct stimuli 
in determining the lateral distribution of the peg. Nott says (p. 
164): “Die meiste inseitige Ausbildung des Wulstes tritt als Ergeb- 
nis zweier heterogener Reize ein. Die localisierte Entstehung 
des Wulstes ist einerseits abhangig vom Gravitationsreiz. Der 
Wulst bildet sich auf der jeweiligen Unterseite. ... . Die ein- 
seitige Wulstbildung wird andererseits auch bedingt durch die 
Krummung des Mutterorgans, derart, dass auf der Konkavseite 
die Bildung des Stemmorgans ausgeldst wird.” 
Francis Darwin? has lately used the peg of the cucurbits as a 
mainstay for the memory theory of plant response. In this, of 
course, he assumed that its development and position are directly 
determined by gravity. Whether gravity acts as a direct stimulus 
to its production and placement is the principal question to be 
tested by the following experiments. 
Methods and materials 
Nott failed to control the factors involved in this problem in 
a way that enabled him to determine the part played by each 
in the lateral placement of the peg. He apparently failed to notice 
the potency of contact of the coats on the one hand, and of the media 
on the other, in arch-production. In the experiments here given, 
to avoid this important influence, except when its effect was to 
be studied, the seeds, whether on the clinostat, centrifuge, or in 
test positions of different inclinations, were freed from the coats 
at the tips and each held by two pieces of cork between which the 
cotyledons were clasped at the central region. The whole appa- 
tatus was kept in the dark and watered by a very fine spray heated 
to 23°C. The spray was formed by forcing the water by means 
of tap pressure through a tank of considerable size kept in a water 
bath at constant temperature, and allowing it to break against a 
plate of glass. In this way contact of both the coats and the soil 
Media is entirely eliminated. Contact, as data later given will 
* Darwin, Francis, New Phytologist 5:199-207. 1906. 
