'
** Haberlandt has briefly described ('Die
Schutzeinrichtungen...Keimpflanze,' 1877, p. 77) this curious structure and
the purpose which it subserves. He states that good figures of the
cotyledon of the onion have been given by Tittmann and by Sachs in his
'Experimental Physiologie,' p. 93.
[page 60]
After a time the apex is drawn out of the empty seed-coats, and rises up,
forming a right angle, or more commonly a still larger angle with the lower
part, and occasionally the whole becomes nearly straight. The conical
protuberance, which originally formed the crown of the arch, is now seated
on one side, and appears like a joint or knee, which from acquiring
chlorophyll becomes green, and increases in size. In rarely or never
becoming perfectly straight, these cotyledons differ remarkably from the
ultimate condition of the arched hypocotyls or epicotyls of dicotyledons.
It is, also, a singular circumstance that the attenuated extremity of the
upper bent portion invariably withers and dies.
A filament, 1.7 inch in length, was affixed nearly upright beneath the knee
to the basal and vertical portion of a cotyledon; and its movements were
traced during 14 h.
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