1910] CROCKER, KNIGHT, ROBERTS—PEG OF CUCURBITS 323 
elongation on the concave side of the hypocotyl. While his 
relating its place of development entirely to the arch is probably 
correct, as we shall see later, his view as to how the arch brings 
about such a placement is crude. We shall see also that his 
claim that the peg does not develop when the seed grows with the 
radicle pointing vertically downward is incorrect. 
FLaHAULT’ claimed that seedlings that developed when the 
- removal of the coats occurred in the normal way were far superior 
to those in which it was prevented by breaking away a portion of 
the lower valve of the coat so that the foot could not get a hold. 
_ This advantage he attributes of course to the hindering of assimila- 
tion by the retained coats. He claimed that the peg develops 
at any point on the hypocotyl necessary to enable it to hold the 
coat. 
Cartes Darwin,’ contrary to FLAHAULT, found that the peg 
develops only at the zone between root and stem. The lower 
face is root, as shown by the presence of root hairs and reaction 
to potassium permanganate, while the upper face is stem. DARWIN 
described a number of experiments, similar to those of TScHER- 
NING, testing the effect of the position of the seed upon the develop- 
ment and functioning of the peg. While Darwin clearly showed 
that the peg is located at the border between root and stem, he did 
not show the stimuli involved in its lateral placement. 
Francis Darwrn® later showed that seedlings of Cucurbita 
ovifera, allowed to germinate on a slowly rotating clinostat with 
a horizontal axis, gave pegs completely surrounding the hypocotyl 
and approximately equal on all faces. He concluded, from the 
inadequate experiments of his father and himself, that gravity 
is a direct stimulus determining the lateral distribution of the peg, 
and that therefore this experiment shows that gravity is continually 
effective on the clinostat and only equalized in its action on the 
several flanks of the exposed object. The conclusion concerning 
+ FLanaurz, C., Sur le talon de la tigelle de quelques Dicotylédones. Bull. 
Soc. France 24: 200. 187 
* Darwin , CHARLES and Francis, The power of movement in plants. pp. 
va New York. 1892. 
ARWIN, of and Acton, E. H., Practical physiology of plants. pp. 192 ff. 
Cambridge 189 
