8 GROWTH OF THE PLANT FROM THE SEED. [lESSON 2. 



the summit of its predecessor ; and each joint elongates throughout 

 every part, until it reaches its full length. The root is not composed 

 of joints, and it lengthens only at the end. The stem in the embryo 

 (viz. the radicle) has a certain length to begin with. In the_ pump- 

 kin-seed, for instance (Fig. 9), it is less than an eighth of an inch 

 long : but it grows in a few days to the length of one or two inches 

 (Fig. 10), or still more, if the seed were deeper covered by the soil. 

 It is by this elongation that the seed-leaves are raised out of the 

 soil, so as to expand in the light and air. The length they acquire 

 varies with the depth of the covering. When large and strong seeds 

 are too deeply buried, the stemlet sometimes grows to the length of 

 several inches in the endeavor to bring the seed-leaves to the sur- 

 face. The lengthening of the succeeding joints of the stem serves to 

 separate the leaves, or pairs of leaves, from one another, and to ex- 

 pose them more fully to the light. 



22. The root, on the other hand, begins by a new formation at 

 the base of the embryo stem ; and it continues to increase in length 

 solely by additions to the extremity, the parts once formed scarcely 

 elongating at all afterwards. This mode of growth is well adapted 

 to the circumstances in which roots are placed, leaving every part 

 undisturbed in the soil where it was formed, while the ever-advan- 

 cing points readily insinuate themselves into the crevices or looser 

 portions of the soil, or pass around the surface of solid obstacles. 



