Another method of performing this experiment is to make a box having one side glass (Fig. 46).  The length and the depth of the box will depend upon the size of the glass you use.  Fill the box nearly full of moist soil and plant seeds of corn and beans and peas at depths of one-quarter inch, one inch, two inches, three inches, and four inches.  These seeds can best be put in as the box is being filled.  Hold each individual seed against the glass with a stick so that when planted they may be seen through the glass.  Protect the seeds and roots from light by using a sheet of cardboard, tin or wrapping paper or a piece of board, and set in a warm place.

Many of the seeds planted only one-quarter inch deep will not sprout because the soil about them will probably dry out before they take from it enough moisture to sprout.  The one and two-inch deep seeds will probably come up all right.  Of the three and four-inch deep seeds, the corn and peas will probably make their way to the surface because they send up only a slender shoot, which can easily force its way through the soil.  The deep-planted beans will make a strong effort but will not succeed in forcing their way to the surface because they are not able to lift the large seed-leaves through so much soil, and will finally give up the struggle.  If any of the deeper beans do get up, the seed-leaves will probably be broken off and the little plant will starve and be dwarfed.  This experiment teaches us that we should plant seeds deep enough to get sufficient moisture for sprouting and yet not so deep that the young seedlings will not be able to force their way to the surface.

Seeds which raise their cotyledons above the soil should not be planted as deep as those which do not.  Large, strong seeds like corn, peas, etc., which do not lift their cotyledons above the surface, can be planted with safety at a depth of from one to four or five inches.

[Illustration:  FIG. 42.  To show how the bean plant gets up.  Notice the curved hypocotyls pulling the seed-leaves or cotyledon out of the soil.]

[Illustration:  FIG. 43.  To show how the corn-plant gets out of the soil.  A slender growing point pushes straight up through the soil, leaving the kernel behind.]

[Illustration:  FIG. 44.  To show the use of the cotyledons.  These are the plants shown in tumbler 2, Fig 42, forty-eight hours after removing the cotyledons from plant B. Plant B, although first up, has been handicapped by the loss of its cotyledons.]

Seeds of carrot, celery, parsley, parsnip and egg plant are weak and rather slow in germinating.  It is customary to plant them rather thickly in order that by the united strength of many seeds they may more readily come to the surface.  This point should be observed also in planting seeds in heavy ground that is liable to pack and crust over before the seeds germinate.

Seed should always be sown in freshly stirred soil and may be planted by hand or with a machine.