The several foregoing arched organs are continually circumnutating, or endeavouring to circumnutate, even before they break through the ground.  As soon as any part of the arch protrudes from the seed-coats it is acted upon by apogeotropism, and both the legs bend upwards as quickly as the surrounding earth will permit, until the arch stands vertically.  By continued growth it then forcibly breaks through the ground; but as it is continually striving to circumnutate this will aid its emergence in some slight degree, for we know that a circumnutating hypocotyl can push away damp sand on all sides.  As soon as the faintest ray of light reaches a seedling, heliotropism will guide it through any crack in the soil, or through an entangled mass of overlying vegetation; for apogeotropism by itself can direct the seedling only blindly upwards.  Hence probably it is that sensitiveness to light resides in the tip of the cotyledons of the Gramineae, and in [page 556] the upper part of the hypocotyls of at least some plants.

As the arch grows upwards the cotyledons are dragged out of the ground.  The seed-coats are either left behind buried, or are retained for a time still enclosing the cotyledons.  These are afterwards cast off merely by the swelling of the cotyledons.  But with most of the Cucurbitaceae there is a curious special contrivance for bursting the seed-coats whilst beneath the ground, namely, a peg at the base of the hypocotyl, projecting at right angles, which holds down the lower half of the seed-coats, whilst the growth of the arched part of the hypocotyl lifts up the upper half, and thus splits them in twain.  A somewhat analogous structure occurs in Mimosa pudica and some other plants.  Before the cotyledons are fully expanded and have diverged, the hypocotyl generally straightens itself by increased growth along the concave side, thus reversing the process which caused the arching.  Ultimately not a trace of the former curvature is left, except in the case of the leaf-like cotyledons of the onion.

The cotyledons can now assume the function of leaves, and decompose carbonic acid; they also yield up to other parts of the plant the nutriment which they often contain.  When they contain a large stock of nutriment they generally remain buried beneath the ground, owing to the small development of the hypocotyl; and thus they have a better chance of escaping destruction by animals.  From unknown causes, nutriment is sometimes stored in the hypocotyl or in the radicle, and then one of the cotyledons or both become rudimentary, of which several instances have been given.  It is probable that the extraordinary manner of germination of Megarrhiza Californica, [page 557] Ipomoea leptophylla and pandurata, and of Quercus virens, is connected with the burying of the tuber-like roots, which at an early age are stocked with nutriment; for in these plants it is the petioles of the cotyledons which first protrude from the seeds, and they are then merely