1910] | CROCKER, KNIGHT, ROBERTS—PEG OF CUCURBITS —_—_333 
marrow it is least so. In the former no two-sided pegs appear 
at 135° deviation or above, while the latter at 180° deviation still 
shows about 8 per cent with two-sided pegs. 
In the exposures with the coats removed, one can see the effect- 
iveness of gravity alone in the one-sided peg-production. It 
must not be forgotten that the effect of gravity in lateral placement 
of the peg is probably entirely indirect and acts through the pro- 
duction of an arch. 
As has been mentioned, Nott thought that not only the develop- 
ment of the peg but its lateral placement is called forth by the joint - 
action of two heterogeneous stimuli: gravity, which causes-the 
development on the lower side of the hypocotyl; and ‘‘organ- 
form” stimulus, which causes the development on the concave side 
ofthe arch. Noz1 compared the second of these to the appearance 
of lateral roots on the convex side of a curved main root. His 
main evidence for the conclusion concerning two heterogeneous 
stimuli is based on his experiments in which he grew seedlings at 
various deviations from the vertical (radicles pointing downward). 
If his statement that any deviation beyond 8°5 always produces 
a one-sided peg were true, his conclusion would be entirely justified. 
Our results, derived by the use of five different varieties of cucur- 
bits, of very different characters so far as peg-development is con- 
cerned, and obtained with greatest care in eliminating all factors, 
except gravity, show that it takes a deviation of not merely 8°5, 
but in every case of more than go’, and in forms like the Boston 
Marrow of more than 135°, to insure a one-sided peg. When a 
Seedling grows in the horizontal position, gravity and the “‘organ- 
form” stimulus certainly are both acting to produce the peg on 
the lower side only, and yet our results show that many seedlings 
thus grown produce two-sided pegs. NOoLt’s two heterogeneous 
stimuli are not adequate to explain these results. This view 
becomes yet less in accord with fact when it is remembered that 
NOLL assumed that gravity could not reach more than 8°5 over 
the lower pole of the hypocotyl, that is, that gravity is not effect- 
ive in inducing peg-development on the upper side of the hypocoty. l 
if the deviation from the vertical is over 825. | 
It has already been pointed out that in Eucalyptus and Cuphea 
