338 BOTANICAL GAZETTE [NOVEMBER 
.go°, thereby avoiding sharp arching. The difference of exposure 
is.marked then only in the early stages, and other exposures with 
go” against 76° and go” against 85° gave no peg-development in 
favor of the 90° either in the pumpkin or squash. It has been 
shown that the effectiveness of geotropic stimulus in orthotropic 
organs is approximately proportional to the sine of the angle, and 
therefore the go° exposure is stronger than any of the others. If 
gravity is effective as a form stimulus in causing the lateral place- 
ment of the peg, we might expect it to be manifested by a larger 
peg-development on the flank exposed at 90°. These experiments 
give no indication of it, and yet it would hardly be expected that 
such differences in exposure would show an effect, since much 
_ greater differences failed to do so in the centrifuge experiments 
described above. It must also be pointed out that, unlike the 
centrifuge experiments, these experiments are rather unsatisfac- 
tory because the arching occurs in favor of the go°, and that factor 
is sufficient, if great, to produce lateral placement of the peg. On 
this account, only angles differing rather slightly can be compared. 
It is evident, however, that these experiments, as do the centr! 
fuge experiments, furnish no evidence that gravity is a direct 
stimulus to the lateral placement of the pég. 
General and summary 
As one sees from the experiments given above, there is 0 
evidence that gravity acts as a direct stimulus to the lateral placement 
of the peg. Certainly, then, Darwin is not justified in using this 
assumption as a main prop to a theory (mnemic theory) which 
itself looks away from rather than toward progress in the knowledge 
of plant response. 
Assuming that all arching is avoided, the following facts seem 
to hold: the peg is to a considerable degree a natural integral 
part of the plant; it develops on all flanks of the hypocotyl approx 
mately equal (granting perhaps that it is somewhat larger 0P the 
broad flanks in many of the cucurbits); it varies in size from the 
very slightest outgrowth appearing in a small percentage of Big 
Tom to the large pegs of the Hubbard squash. : 
It may be laid down with the formation of the seed, a5 
