322 BOTANICAL GAZETTE [NOVEMBER 
MreseEt! and TirtMAn? very early showed the presence of this 
organ throughout the Cucurbitaceae. While it is well developed 
in the epigean forms, it is very rudimentary in the hypogean forms, 
such as Megarhiza californica and Sicyosperma gracilis. The 
organ is by no means limited to the Cucurbitaceae, but appears in 
various genera of a number of families: Mirabilis, Oxybaphus, 
and Abronia (Nyctaginaceae), Martynia (Martyniaceae), Lind- 
heimera (Compositae), Mimosa (Leguminosae), Tribulus (Zygo- 
phyllaceae), Eucalypius (Myrtaceae), Cuphea (Lythraceae), vie 
While in Cucurbitaceae the peg appears only after germination 
has progressed considerably, in other forms, as Eucalyptus and . 
Cuphea, it is already laid down as a complete ring in the mature 
seed, and with germination completes its development. 
TitTMAN recognized the biological significance of this organ 
the Cucurbitaceae, and showed that it appears only on the lower 
side of the developing hypocotyl. 
TSCHERNING? gives a rather full description of its histology 
and physiology. He states that it is a parenchymatous out- 
growth. While the greater diameter of the parenchymatous cells 
in other parts of the hypocotyl is longitudinal, in the peg zone it 
is radial. The number of layers of cortical cells is also somewhat 
greater at the peg zone. TsCHERNING describes the effect of the 
position of the seed during germination upon the development and 
functioning of the peg. He says that when the radicle points 
~ vertically downward the swelling does not occur, and the cary” 
ledons push above the ground still bearing the coat. With radicle 
pointing vertically upward, the peg develops on the concave side 
of the arch, but does not remove the coat. When the seeds are 
planted on edge, the peg develops on the concave side of the arch 
and wedges between the two valves of the coat, thus succeeding 
removing a considerable percentage of them. When the seeds are 
planted on a flat face, the peg develops on the concave side of the 
arch and attaches itself securely to the lower valve of the coat, 
thereby insuring its removal. TscHERNING emphasizes the devel- 
opment of the peg on the concave side of the arch, and speaks of 
it as a lateral pushing out of the cells due to the inhibition the 
» % 2,3 See under Nox, footnote 8. : 
