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This part would ultimately form
the upper end of the hypocotyl, after it had grown straight and vertical.
Had the seed been properly planted, the hypocotyl at this stage of growth
would have been deeply buried beneath the surface. The course followed by
the bead of the filament is shown in Fig. 28. The chief lines of movement
from left to right in the figure were parallel to the plane of the two
united cotyledons and of the flattened seed; and this movement would aid in
dragging them out of the seed-coats, which are held down by a special
structure hereafter to be described. The movement at right angles to the
above lines was due to the arched hypocotyl becoming more arched as it
increased in height. The foregoing observations apply to the leg of the
arch next to the cotyledons, but
[page 41]
the other leg adjoining the radicle likewise circumnutated at an equally
early age.
The movement of the same hypocotyl after it had become straight and
vertical, but with the cotyledons only partially expanded, is shown in Fig.
29. The course pursued during 12 h.


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