TEXTBOOK OF BOTANY 



the use of an ordinary lens. The important fact for us to 

 notice is that the seed consists of a small plant (the embryo) 

 which is ready to continue its growth as soon as conditions 



FIG. i. A, side view of a squash seed ; B, a lengthwise section through 

 the middle of a squash seed ; a, scar, showing the place at which the seed 

 was attached; b, seed coat; c, endosperm; d, seed leaves; e, plumule; 

 /, radicle. 



are favorable ; and also of some surrounding layers which 

 protect the embryo. 



2. Germination of the Seed. If some squash seeds are 

 placed in moist sand or sawdust and are examined from time 

 to time, it will be found that they gradually swell. This is 

 because water is taken in both by the seed coat and by the 

 embryo. After a few days the seed coat begins to crack; 

 the crack starts at the micropyle and extends down the two 

 edges of the coat. Then the end of the radicle begins to push 

 out through the opening in the seed coat (Fig. 2, A). This 

 is because all parts of the embryo, and especially the radicle, 

 are beginning to grow, and there is no longer room for the 

 whole embryo within the seed coat. As soon as the end of 

 the radicle is well outside the seed, it turns downward and 

 grows in that direction. This downward growth pushes the 

 tip of the radicle farther into the soil. From the radicle, 

 therefore, is developed the primary root of the young plant, 



