LIVING CONDITIONS; THE SEED 67 



58. The seed. We may know something about the conditions 

 that are necessary for the sprouting of seeds, and still be unable 

 to answer the question, Why do seeds sprout? A part of the 

 answer is, of course, in the nature of the seed itself. 



We have already seen that a seed originates in a flower 

 (sect. 36). If you examine the outside of any seed, you can usu- 

 ally find a scar that was left when the seed broke away from 

 the little stalk by which it was fastened inside the ovary, or 

 fruit. Very often you can also see the tiny hole (the micro pyle, 

 see m, Fig. 19) through which the pollen tube found its way to 

 the embryo sac. The seed may absorb water through this hole, 

 but it does not seem to be of any importance after the seed is 

 ripe. The coat of the seed, which in some cases has more than 

 one layer, is evidently a protective cover. In many plants, how- 

 ever, the protection is furnished by the fruit wall— in common 

 nuts, for example. After you remove the coat you can find the 

 part of the seed that is really important in the life of the plant. 

 In fact, you w^ll find here a young plant, or embryo, so that we 

 may say that a seed is an embryo with its covering. 



59. The embryo. If you recall that ordinarily we think of a 

 whole plant as being made up of root and shoot (see Fig. 5), 

 you can soon see that the embryo is indeed such a plant. After 

 soaking some seeds of pumpkin, beans, peanuts, and other 

 species in water, so that you can easily open them up and take 

 them apart, you will find two fleshy parts that make up the 

 bulk of the embryo. These are really special kinds of leaves, 

 although they do not resemble the ordinary leaves of these 

 plants. Now bend them aside carefully without breaking 

 them off, and you will see that they are attached to a short, 

 stalklike piece. One end of this rod tapers to a point; the 

 tip of this corresponds to the root, although it does not branch. 

 The rest of the main stalk, with its two large outgrowths, 

 corresponds to the shoot. The upper end of this may be 

 enlarged to a little knob or bud. In the embryo of the bean 

 you can make out two small but distinct leaves overlapping 

 a tiny bud. 



