=206. Structure of the pumpkin seed.=—The pumpkin seed has a tough papery outer covering for the protection of the embryo plant within. This covering is made up of the seed coats. When the seed is opened by slitting off these coats there is seen within the “meat” of the pumpkin seed. This is nothing more than the embryo plant. The larger part of this embryo consists of two flattened bodies which are more prominent than any other part of the plantlet at this time. These two flattened bodies are the two first leaves, usually called _cotyledons_. If we spread these cotyledons apart we see that they are connected at one end. Lying between them at this point of attachment is a small bud. This is the _plumule_. The plumule consists of the very young leaves at the end of the stem which will grow as the seed germinates. At the other end where the cotyledons are joined is a small projection, the young root, often termed the _radicle_. =207. How the embryo gets out of a pumpkin seed.=—To see how the embryo gets out of the pumpkin seed we should examine seeds germinated in the folds of damp paper or on damp sphagnum, as well as some which have been germinated in earth. Seeds should be selected which represent several different stages of germination. [Illustration: Fig. 88. Germinating seed of pumpkin, showing how the heel or “peg” catches on the seed coat to cast it off.] [Illustration: Fig. 89. Escape of the pumpkin seedling from the seed coats.] =208. The peg helps to pull the seed coats apart.=—The root pushes its way out from between the stout seed coats at the smaller end, and then turns downward unless prevented from so doing by a hard surface. After the root is 2-4_cm_ long, and the two halves of the seed coats have begun to be pried apart, if we look in this rift at the junction of the root and stem, we shall see that one end of the seed coat is caught against a heel, or “peg,” which has grown out from the stem for this purpose. Now if we examine one which is a little more advanced, we shall see this heel more distinctly, and also that the stem is arching out away from the seed coats. As the stem arches up its back in this way it pries with the cotyledons against the upper seed coat, but the lower seed coat is caught against this heel, and the two are pulled gradually apart. In this way the embryo plant pulls itself out from between the seed coats. In the case of seeds which are planted deeply in the soil we do not see this contrivance unless we dig down into the earth. The stem of the seedling arches through the soil, pulling the cotyledons up at one end. Then it straightens up, the green cotyledons part, and open out their inner faces to the sunlight, as shown in fig. 90. If we dig into the soil we shall see that this same heel is formed on the stem, and that the seed coats are cast off into the soil. [Illustration: Fig. 90. Pumpkin seedling rising from the ground.]