How Seedlings Come up from the Ground
The life in a dry seed. For this study we shall use seeds of beans, peas, corn, pumpkin, sunflower, and buckwheat. You may use some other seeds if they are more convenient, but these are easy to get at feed stores or seed stores. If you did not know that they were seeds of plants, you would not believe that these dry and hard objects had any life in them. They show no signs of life while they are kept for weeks or months in the packet or bag in a dry room.
But plant the seeds in damp soil in the garden or field during the warm season, or plant them in a box or pot of damp soil kept in a warm room. For several days there is no sign that any change is taking place in the seeds. But in a few days or a week, if it is not too cold, some of the surface earth above the buried seeds is disturbed, lifted, or cracked. Rising through this opening in the surface soil there is a young green plant. We see that it has life now, because it grows and has the power to push its way through the soil. The dry seed was alive, but could not grow. The plant life was dormant in the dry seed. What made the plant life active when the seed was buried in the soil?
How the corn seedling gets out of the ground. One should watch for the earliest appearance of the seedlings coming through the soil. The corn seedling seems to come up with little difficulty. It comes up straight, as a slender, pointed object which pierces through the soil easily, unless the earth is very hard, or a clod or stone lies above the seedling. It looks like a tender stem, but in a few days more it unrolls, or unwinds, and long, slender leaves appear, so that what we took for a stem was not a stem at all, but delicate leaves wrapped round each other so tightly as to push their way through the soil unharmed. What would have happened to the leaves if they had unfolded in the ground?
How the bean behaves in coming out of the ground. When we look for the bean seedling as it is coming up we see that the stem is bent into a loop. This loop forces its way through the soil, dragging on one end the bean that was buried. Sometimes the outer coat of the seed clings to the bean as it comes from the ground, but usually this slips off and is left in the ground. Soon after the loop appears above ground it straightens out and lifts the bean several inches high. As the bean is being raised above ground the outer coat slips off. Now we see that the bean is split into two thick parts (cot-y-le'dons ), which spread farther and farther apart, showing between them young green leaves, which soon expand into well-formed bean leaves.
The pea seedling comes up in a different way. The stem of the pea also comes up in a loop. As it straightens up we look in vain for the pea on the end. There are small green leaves, but no thick part of the pea which was buried in the ground. This part of the pea, then, must have been left in the ground. When we have seen how the other seedlings come up, we can plant more seeds in such a way as to see just how each seed germinates, and learn the reason for the different behavior of the seedlings in coming from the ground.
The pumpkin seedling also comes up in a loop, and on one end of the loop, as it is being lifted through the soil, we see two flat, rather thick parts. Together they are about the size of the pumpkin seed. By looking carefully we may sometimes find the old shell, or seed coat, still clinging to the tips of these parts of the seed; the shell is split part way down only, and so pinches tightly over the tips. Usually, however, it is left empty in the ground.
It will be interesting later to see how this little pumpkin plant gets out of its shell. It usually escapes while still buried in the soil. As the loop straightens out, these two thick portions spread wide apart in the light and become green. There are little lines on them resembling the "veins" on some leaves. Are these two parts of the pumpkin seed real leaves? Look down between them where they join the stem. Very young leaves are growing out from between them.
The sunflower seedling. The sunflower seedling comes up with a loop, dragging the seed on one end. The shell, or seed coat, is sometimes left in the ground, because it splits farther through when the root wedges its way out. But often the seed coat clings to the tips of the cotyledons until the plant straightens. Then the cotyledons usually spread far apart. The seed coat of the pumpkin sometimes clings to the tips of the cotyledons until the sunlight pries them apart.
The buckwheat seedling. This also comes up with a loop, and we begin to see that this way of coming up is very common among seedlings. The seed coat of the buckwheat is often lifted above ground on one end of the loop. It is split nearly across. Through the split in the seed we can see that there are leaves packed inside very differently from the way in which the cotyledons of the pumpkin and sunflower lie. The buckwheat cotyledons are twisted or rolled round each other. As the seedling straightens up they untwist, and in doing this help to throw off the coat.