. Biology and human life. Biology. LIVING CONDITIONS; THE SEED 69. 60. Food in seeds. The concentrated food found in seeds of common plants is of interest to us in three ways: First of all, we may infer that this food is actually used by the young plant until it is able to provide for itself. That this is a sound infer- ence may be tested by separating from several seedlings the "food ; Next we can observe that the cotyledons in such plants as the beans and peas do actually shrivel away as the plant becomes larger. The con- tents of the corn grain also dis- appear as the seed
. Biology and human life. Biology. LIVING CONDITIONS; THE SEED 69. 60. Food in seeds. The concentrated food found in seeds of common plants is of interest to us in three ways: First of all, we may infer that this food is actually used by the young plant until it is able to provide for itself. That this is a sound infer- ence may be tested by separating from several seedlings the "food ; Next we can observe that the cotyledons in such plants as the beans and peas do actually shrivel away as the plant becomes larger. The con- tents of the corn grain also dis- appear as the seedling develops. Finally, by means of chemical experiments we can see that the changes taking place in the food masses of the seedlings are of the kind that we should expect to find if the food were actually being transported to the growing portions (see section 105). 61. Seedlings. Examine a few seeds that have been planted two or three days, and you will see that the hypocotyl has emerged and is assuming the appearance of a root. At the other end of the embryo you may see the unfolding epicotyl. If we examine different stages of peas, squash, oats, corn, beans, and so on, we shall be able to see a great variety of methods by which the young plant crawls out of its covering and establishes itself in the soil (Fig. 35). Large seeds, containing a large amount of reserve food, are apparently at an advantage, since they may develop more root and more shoot before they are overtaken by the necessity of providing themselves with food. We should therefore expect that plants with large seeds would be, on the whole, more Fig. 34. Seeds with endosperms /, asparagus; 2, poppy: 3, pine; 4, maize, or Indian corn. In some kinds of seeds the cotyledons are very thin. In such cases we usu- ally find that there is a great deal of food material surrounding the embryo, whereas in seeds with fleshy cotyledons there is food packed within the cotyledon. The food packed around the seed is called endos
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